Scratched xbox game what should i do ?

so today i bought fifa 11 .as i was playing it .it said unreadable disk,i opened the tray and there was nothing wrong with it .i put it back in the xbox than accidently moved my xbox while it was playing and it scratched the cd in a circular motion. i bought it at a game store called.microplay.i want to ruturn it bu im afraid they wont take it back. if they dont do .i was thinking of going to blockbuster renting the same game and switching the games .and just say that the game was like that when i got it