If the scratch is accidental, AppleCare + may fix it at a reduced cost, but you need to ask Apple. People who respond here are your fellow end users and we cannot provide "official" answers.
The only fix is to replace the entire upper display unit. It is a sealed unit and individual components like the screen cover cannot be separately replaced. parts and installation can cost US$500-650 if not covered by Applecare based on owner reports here.
ANY attempt to migrate the scratch with home remedies will make it worse. I recommend living with it if AppleCare does not cover it.