Well, if you can, give it a good wipe down anyway and see what happens. If you see any improvement, even a little, you'll know for sure it is just dirt and therefore an easy fix. From what I can tell in the pic, it looks like maybe the space bar is what is touching the screen?
The person in this post had a similar problem and it was indeed scratched, but looks way worse than yours:
https://forums.macrumors.com/threads/2015-rmbp-screen-scratched-by-keyboard.1945130/
That person had the screen replaced under warranty but it happened again shortly after. Replies to that post suggest that the keyboard is sitting too high due to misalignment from the factory. Since yours is a 2012 model, it may be too late to have any repairs done under warranty, but definitely something you might want to check out or at least take it to an Apple store to see what they can do for you or what they would recommend.
To answer your original question, I don't know of anything you could use to mask the damaged appearance, sorry. Auto body scratch cover-up, or even WD-40 comes to mind, but I don't think that would work for scratched display. Hope someone else here is able to come up with a better solution for you.