Ryan Maloney shows three ways to paint inside a shape without going over the edges: use layer selection to confine strokes to one layer, enable Alpha Lock to lock transparency, or create a clipping mask to link a new layer to the shape below.
Chapters
If you have a shape drawn in Procreate and you want to draw over that shape, but you don't want to overlap the edges, here are 3 ways to do it. The first way is to select the layer. Open up your layers palette, tap the thumbnail of the layer you're working on, hit select. Now you just draw on top of the shape and you won't go over the edges. The second way is alpha lock. I'm going to go into my layers, hit alpha lock. I can draw seams here and not go over the edges. The third way to do it is to create a clipping mask. Go to the shape you want to draw on, hit new layer, tap that new layer thumbnail, go down to clipping mask, and you'll see this little arrow pointing to the bottom layer is there. Now when I draw, I'm not drawing anywhere outside of that layer. I'm drawing inside of it.