Since the dome is still fully functional and a scratch is caused by some sort of accident, a scratch is not considered a malfunction of the part, therefore it is not covered by warranty. What you can do is clean any dirt or scuff marks that are in the scratch of the acrylic. This can be done using an alcohol wipe or rubbing alcohol and a rag. Once the scratch has been cleaned out as much as possible, take a standard/classic toothpaste such as Colgate Cavity Protection and apply a dab of it to the scratch, as you would a wax, and rub it into the scratch in a circular motion. Then take a dry piece of your rag and buff out the paste. This should help to further clean and fill in the scratch.