Please help Xbox Live people?

I just recently bought LA Noire, and started downloading the Slip of The Toungue add on I got with it. I started to download, typed the redeem code and everything, but realized I was downloading on the Hard Drive (I wanted it on a memory card) so I backed out. I tried again and it said the code was invalid. I went to my hard drive and it says Incomplete Game or Unknown game or something. How do I reverse all this and get my add- on back so I can download it on what I want? I don't know what to do. Thanks guys.