Very easy to to use some clear box tape and cover the outside edges of the wing. I have also used excess decal flashing and cut the wing side shape out, then stuck decals on that and placed it all on at once. Double protection 😉
That is where pinstriping tape comes in handy. It's easy to follow the body lines.
Liquid mask works great, but it's not really meant for doing straight lines. It's more for designs that you cut into it after set, and masking difficult areas.
If you want nice clean stripes, use vinyl masking tape. You can grab it off Amazon. When spraying, lightly dust the edges of the masking tape with your first coat or two. Never spray towards the tape's edge. Spray straight down on the tape. Let it dry before doing the next coat. This will help...