did you wet sand it? wet sanding is important as it will smooth out the lights, rather then dry sand paper, start from rough then move to fine. Then using a polishing clothing, apply about 10cent coin amount on the cloth, spread it over the lights, next thing you would do is keep rubbing the cloth hard, you will eventually melt rough layer away. Remember to change to a clean part of the towel and rub hard, until you see a clear coat shine through.

btw it'll dull up after you wet sand it, it doesn't matter, as long as the lens is clear, you can then apply polish and start polishing it