If you can feel it with your fingernail then, unfortunately, no amount of polish will remove it, not even jewellers rouge which is a fine abrasive. Also worth bearing in mind that anything too abrasive will form a slight hollow on the screen, in effect creating a concave lens. This is not good for looking through whilst driving, especially at night.
If you can't feel it then hopefully you'll be able to get away with the suggestions mentioned above.
If it's really bad, just claim for a new one from your insurance company.