Work-in-Progress: Stencils on Tees

So, my current WIP is putting stencils on tees. As I mentioned before, I am new at the whole creating custom content thing, so I'm learning from the ground up. Right now, stencils.

I made some stencils to use. They looked fine in GIMP, but they look off in-game. The images are more narrow than they're meant to be, the words are kind of pixelated and have some unknown white stuff around them that, while I can't see it at all in GIMP, is definitely there in CAS.

The other issue I'm grappling with, I will own, is completely my fault. I cannot figure out how to change the presets of the shirts. Like that picture, before I fixed it in CAST was like...that purple shirt with the weird diagonal pattern. (You know what I'm talking about.) Ideally, I want to change the patterns of the shirts that the stencil is on, so by default, the presets work better with the pattern. I like the shape of the shirt, etc, but that purple pattern is so vile, it really detracts from any kind of stencil.

So, I'mma keep working on how to fix it. Feel free to shout out any suggestions.