How bad is the scratch..?? if it is tiny and thin take a butane torch very quickly over the scratched area, back and forth until it dissapears, I have polished quite a few peices of plexi in my day If it is very deep or very bumpy take around a 2000 grit to the intire surface and make it look foggy and make sure you go deep enough get ride of the scratches and again take a butane torch back and forth accross it and watch the scratches dissapear before your eyes