It has to be the right size to properly wrap on the car. Also, where did you get that black mask? It doesn't align with the UV mapping at all, and that is why you are getting black spots on your car. Remove the black overlay and use the one from the Master Skinnerz Pro Skinning Kits.
Those missdrawed lines on the right side, outside actually, make the resolution go wrong. Also, there seems to be an white border going around the skin that might upset the mapping too.
i see the problem. it was origonaly one of the master skinnerz pro kits. I put it into appleworks to draw the lines(I can't find a line drawing tool in photoshop elements 4.0) an I suppost appleworks resized it. I though the skin was a cool idea when I drew all over a template