never used ibis paint before?
here's the perfect place to start!
MAKING YOUR OWN CANVAS.

when you open the app, you'll be greeted with this screen (or a short slide by slide kinda tutorial about the app if it's newly downloaded). click my gallery

then you'll be opening the place where your works will be stored. to make a new work, click the + button on the lower left corner which will then open a pop-up window.

you can see that there are premade canvas sizes you can use (you scroll down for more) but none of those fit a wattpad cover so you'd have to manually put it in :)

you'd want to focus on that area and input 512 x 800 (or any variant [i now usually use 1024 x 1600] of your choice) then click OK and you'd have a canvas to work on :))