So went in to Game Stop and saw a used copy for $2.99. Never played it, enjoying it so far... however I am more concerned with the back of the disc having a good bit of wear. A game store up the street from me offers disc repair, I am assuming with a skipdoctor or whatever. My question is does it actually work? I mean there aren't actual deep scratches or anything just a few surface marks.

If you are playing it already it shouldn't be a problem. Installing it will tell you if it has problems. Sometimes if a game has scratches it could work for all but one single part of a level and its enough to hinder progress.

Try to install it, that will tell you if it works perfect or not.