The thing is, if you look head-on at a Great Ball, the lines go straight, as in there is no curving besides going around the ball. Which means, I actually messed up on the design anyway. >.< Ugh, this is getting frustrating…
EDIT: Of course, one alternative is to use the game's Pokéballs, but (a) they're not the same style and (b) they're 18x18, which would be an entire 16 extra pixels wider for mods.