The info states that you should receive your code for the Omega boss battle within 1-2 days from the time you were charged and the game shipped. So, keep on checking your email, you should receive it soon.
As someone esle said, check your spam. You should have 2 emails, one with the Omega code and $10, and another one with anotuher $10. One came through my homail acct fine, the other went to my spam folder.