If it's from the console being moved whilst turned on, there really isn't a way. That's a laser burn and it's etched in there pretty good.
On the bright side, if Wal Mart has it in stock, take it there, say it doesn't work, they'll exchange it for a copy of the same game 90% of the time. Regardless if you bought it there or not/receipt or not. Just make sure they don't know you didn't.
I really enjoyed Mirror's Edge, it was a great game, and worth the $20 I paid for it. They implemented everything fairly well and it was nice and fast paced. A bit short, however. The time trials are fun and add challenge, as well as the 'hard' mode, which disables runner vision (essentially the system telling you where to go).
However, I don't really recommend buying it, just rent it, beat it, and get all the achievements out of it that you like, because honestly, you probably won't play it again after that. Though that's just my opinion, as I didn't. You never know. I highly recommend at least renting prior to buying.