What color is the paint? Is it metallic? Is it pearl like? Those will be your most difficult to match. And if you use too much paint, yeah it will apear darker.
You did good by not using the "paint brush"(for lack of a better term)...its useless! I prefer artists detail brushes, you can usually find them inexpensively. Use as lil paint as possible, and repeat if necissarry...but dont glob it.
Alright now comes the hard part...find some 1000 gritt wet sand paper, keep the surface wet and lightly wet sand that portion, follow with a high quality wax. But be careful, you dont wanna go to deep on the good paint!