Have you tried using a polishing compound on it?
I am going on the premise from back in my army days when my brass belt buckle got a scratch you could see and feel. About an hour of hand polishing with Brasso completely removed the scratch. Now I am not saying use Brasso, I was just giving you the idea behind polishing.
To work on glass, you will need polishing compound, jeweler's rouge or whitening toothpaste (gel toothpaste does not work). Using a lambs wool buffing pad you can either buff the scratch by hand using a circular motion or with an electric buffer on medium speed.
If you are willing to spend a little more cash there is
Eastwood’s Professional Wind Shield/Headlight Kit for $49.99
Good luck