You can put too much clear coat on, but keep in mind that unless you are very good at painting and have a proper downdraft booth you will most likely get areas that have runs or orange peel, or the dreaded insect enbalmed in clearcoat! Assuming you used a clear with a hardener, you should most likely sand and buff the car, and this will thin out the thickness of the clear coat. If you don't have much experience color sanding you are better off to use a finer grit of sandpaper, say 2000, to avoid making big scratches. Use wet sandpaper, and a sanding block or pad- don't use your bare hand, it will leave "grooves" in the clear. Use a rubber sqeegie to dry off the area you just sanded- if it has a matte finish (no orange peel or pinpricks) stop sanding. After that either hand rub the finish or use a buffer. I suggest you pick the brain of the local automotive paint store in your area- they should know what works with the paints they sell.
Be patient- rubbing out a finish is very time consuming- and watch you don't sand thru the edges! Good luck.