Sandpaper has grit. Toothpaste has grit. So using both is a double whammy. Try one of the polishing systems out there which start at 2500 grit and in 6 steps goes up to 12000 grit. Then use something like Novus #2 to remove any marks, following a coat on The Treatment Model Car Wax. Don't forget a small squirt of Dawn in you water for better sandpaper lubrication.