But how…?
Clean the disc with a soft cloth (the ones that are made for electronics) and hold the disc from the edge, and wipe it from the center outwards. You can use ethyl alcohol to clean it or a commercial CD cleaner to clean any stubborn smudges.
You can also try cleaning the lens of your machine. Dunno what machine you’ve got, but just google something like, "cleaning PS2/PS lens" with whatever system you’re using.
If you have a bum burned copy, then I guess your other choice is to buy another (real) copy of the game.