try checking normals, when working with planes the normals got inverted eventually.
go in Normal menu and select invert where it should,
too see where the normals are flipped go to the viewport lighting menu and uncheck the two side light box.

Well when inverting the normals, it makes my object black. I don't think that's right.

This might be because the texture has a wireframe in it outlining the UVs
This wireframe is nice if you want to see whats going on when painting the texture, but you have to remove it before exporting the texture.

Sorry for not clarifying, it was a transparent wireframe type of deal, but I figured it out,