If you redeemed it you dun goofed. I am assuming you are good for playing, just put the code you will be emailed on your XBL account. I'm not sure you will get the beta loot though if you don't have the correct gamer tag linked to a Bungie account with a redeemed beta code. You could go beta code hunting or do the amazon trick (pre order, get code, cancel) and redeem the new code on the right account.