I use one of those $2 buffing wheels from eBay, put it in a drill, mix some toothpaste with a little water and less than a minute later is as good as new, Polywatch or other pompous expensive BS don't hold a candle to this method. Of course the watch needs to be waterproof first and the bezel masked with tape. If the scratch is to deep you need to use some sandpaper first to level it out.
If the scratches we're talking are just hairlines, I advise you to get used to them and don't touch them yet. Acrylic will scratch at the slightest touch, even by wiping it with a paper towel, I bet you will collect a lot more scratches pretty soon, if you buff it every time you get a hairline you will soon be left with no crystal to buff.