ive been doin the paint touch up work for about 2 months now and i love it!! i pretty much have everything down good, but smetimes i tend to sand to deep into the bumper leaving a ring shaped look after i put my basecoat on. on the darker color cars, the ring usually covers up when i clearcoat, but on lighter colors such as silvers and golds, the ring shows. i sand with 220, 400 then 1000. Could it be i am not sanding the damaged area out far enough? How do i prevent this problem?

You may need to feather out your body filler more. Then use your etching and surfacing primer and feather them out as well. If you sand through too far in your primer it can leave marks in your body color. If you sand through you need to re-prime it and re-sand it. In addition make sure you are using a guide coat that may help you from sanding through. I hope this helps you out.