looks like you just straight up did normal paintbrush, opacity 100%. you should try doing an overlay, or even normal (paintbrush) but set the opacity real low, and then do multiple coats. as far as lowering, im not that great at that. Normally, i just scale up the wheels a bit after selecting them. Ive just recently become a little better at making selections so maybe select the whole body of the car, and lower it down on the wheels. I am still learning as well.