Doesn't quite follow the timeline, but I thought this would be cute.
  "There was an arrow heading for Stormfly, so I blocked it." She shrugged.
   "With your leg?"
   "I'm fine. It's just a flesh wound."
******Later that night******
   Astrid sat up with a wince, grasping her thigh.  It was throbbing and burned like changewing acid had been poured on it.
   She threw the covers off and was surprised to see that her arrow wound had bled through its dressing and straight through her leggings.
   "Oh for the love of-!" Astrid flew back into the pillows and groaned. She had lied to Hiccup. It wasn't just a flesh wound. It was much deeper. And it turns out, she couldn't dress it herself.
     Stormfly sat up, roused by Astrid's groaning, and gave her rider a look that said "I told you so."
   "Stormfly I took that arrow for you, so hush."
   Astrid got out of bed, feeling butterflies erupt in her stomach as she did so. She opened the door to her hut as quietly as possible, then started limping next door.
   *****
   Hiccup was just getting ready to put out his lantern and go to sleep when he heard the knock at his door.
   "Hiccup, are you awake?"
   Astrid? What is she doing up so late? Hiccup walked over and opened the door.
   "What's wrong?"
   Astrid blushed deeply and pulled up a length of her skirt to reveal the bloody spot in her leggings.
   "Maybe it wasn't..just a flesh wound. I-I think the arrow chipped when I pulled it out."
   "Astrid.." He gasped, shaking his head. "Why didn't you let someone look at it?"
   "I didn't want to be a bother."
   Hiccup pulled her inside and closed the door. Afterward he rumaged under his bed until he found a wooden box with some medical stuff in it. All the riders had one.
   "C'mon, you can sit on the bed." He patted it, then sat on the ground and opened the box.
   Astrid tentatively walked over and sat down on his bed near the headboard. It smelled like him over here, which she found odly comforting. When she came out of her thoughts she saw Hiccup staring at her awkwardly with some medical wipes in his hand. He cleared his throat and gestured at her leg.
   "Um.."
   "Oh! Right." Astrid blushed for the second time that night as she pulled her leggings down. She felt exposed, even though her skirt still covered everything important. Besides, it wasn't like Hiccup hadn't seen her before. But it still just felt...awkward. She looked up to see Hiccup blushing too.
   "What?"
   "Nothing." He said quickly, skooting closer and removing the dressing Astrid had applied, which was soaked in blood. She grimaced as he began wiping the blood away and he glanced up at her apologetically.
   As he continued to clean the outside of the wound and the surrounding area, it became clear that there was definitely a piece of arrow still in her leg.
   "See this is why we don't block arrows with our legs."
   "You would have done the same thing!" Astrid defended, crossing her arms and turning away from him. "Actually, you have. You stood in front of the Skrill when all of the dragon hunters were aiming for it!"
    "That was different!"
    "How?"
    "They hadn't actually fired yet." He said after a brief pause.
   "You hesitated." Astrid smirked triumphantly. When Hiccup didn't reply and started looking for something in his box again, her face fell.
   Hiccup found the tweezers he was looking for and brought his hands up to her leg again.
   "Are you mad at me?"
   This made him pause. He had to think about it for a moment, because he didn't really know.
   "Hiccup?"
   "No." He said finally. "No, I'm not mad at you. I'm mad that you're hurt."
   "Is there a difference?"
   "Yes." He nodded. "I've only been mad at you twice in my life, and this does not make it a third. I ..." He tilted his head side to side, finding the best way to word his next sentence. "I just wish I didn't have to see you hurt so often. It makes me sad."
   Astrid's eyes widened. "It does?"
   "Well...yea of course it does."
   She smiled and tilted her head to make better eye contact with him. "It makes me sad when you get hurt too."
   "Well," Hiccup ran a hand through his hair, presumably to hide his now very red face. "Let's get the rest of the arrow out of your leg, hmm?"
   Astrid nodded. "Just be gentle."
   He rolled his eyes at her playfully. As if he wasn't always gentle with her.
   Unfortunately, the broken piece of arrow in Astrid's thigh did not want to come out. Hiccup had ahold of it with the tweezers, then it slipped.
   Without really realizing what she was doing, Astrid reached out and grasped Hiccup's arm. She had been dealing with the pain pretty well so far, but that had hurt like hell. Her eyes were squeezed shut and her lips pulled together tightly.
   "I'm sorry." He cringed. "I know it hurts. But I'm almost done."
   She nodded in reply, still not opening her eyes.
   "Ready?"
   "Just do it."
   This time Hiccup made sure he had a good grip on the fragment. He pulled it out, then immediately placed a bandage over top the wound.
   She let out a sigh of relief and held the cloth in place while he taped it.
   "There. All better." He patted her knee gently. "Now try not to exert yourself tomorrow."
   "Yea, yea."
   "Here, stand up."
   She did as he said, and blushed deeply when he pulled her leggings up. When he reached her waist he was able to let go and stand straight.
   Astrid kept forgetting how tall he had gotten. Especially when he was this close to her. He pecked her forehead, then looked at her very seriously.
   "I mean it, Astrid. No training for at least two days."
   "What?" She plopped down on the bed again. "No, that's not fair! I'm training, you can't stop me."
   "Do you want to get an infection? Because then you'll be laid up in bed for weeks. And it'll hurt a lot worse than it does now, trust me."
   "No.." Astrid sighed in defeat, crossing your arms again. She knew she should listen to him. It was just extremely frustrating not to train.
   "That's what I thought." Hiccup smirked.
   "I hate laying around." She pouted.
   He couldn't help but chuckle at her pouty lip. "I know, but you'll survive. I promise."
   "That's easy for you to say! You get to go and train with your dragon tomorrow." She suddenly grabbed his arm and threw him to the ground.Not hard enough to hurt him, but not really as athletically well either. "See? I can still lay you flat."
   Hiccup grinned from the ground as she placed her foot on his chest.
   "What is that face for?" She giggled.
   "Oh, nothing."
   "What?" She demanded.
   "Nothing. Just, this is usually the part where you kiss me, and I really like that part."
   Her eyes squeezed to slits, although she still couldn't stop smiling. "You do realize if my thigh wasn't throbbing right now, I would attack you right?"
   "Oh, yes, I'm fully aware." Hiccup chuckled.
   "Oh you-!" Astrid removed her foot and jerked her thumb "Get up here!"
   He stood up, still smirking. Astrid seized the front of his tunic and yanked him right to her, smashing her lips into his.
   "That's for making me stall on training."
   She kissed him again, as tradition this one was longer. "That, is for fixing my leg."
    "I love you."
    "I love you too, Muttonhead."