You used the bodykit from daloonie and put the decals on top of those layers. For the best effect you should put it under it. Search in daloonie`s layer were your layer give the best possible effect. So the decal layer has the same dirt and shape as the car. Makes it so more realistic.
Play around with it, as stated in the bodykit made by daloonie. You need to open up all the layers to see the hidden once, just klick on the arrow in the layer to see them. Now youll see the shape/highlighted/dirt layers. By changing them in position up or downwards you change the way the car looks. The same goes with your decal. Play with it, and see what gives you the best result. Skinning isnt about putting something on a bodykit, but playing tweaking it until your satified.