Don't worry! I did lose, so tonight I called my local Gamestop. The employee said that as long as you pick it up from the store you pre-ordered it from(duh)they will have it on the computer. I was worried and I saw some other people were too so this was a PSA to the people who wanted this Information. BTW, this was the US Gamestop.
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Thats what I did with Halo 3 lol..just give em your phone number and you're fine