ginswoo: well I bought a game at work this morning since it was on sale and created the account at the same time it took me to the download page and I logged out. I just recently went on to download the game and my email that I used wont let me log in but my username is still taken and my credit card was charged the $5 so I know its there.
Have you gotten a confirmation email for your order? If not, it sounds like you mistyped your email address during account creation. In which case you're more or less out of luck, I'm afraid.
You can try writing GOG support, but I'm not sure they'll be able to help you in that particular scenario.