So I go to my local game stop today and buy Sins of a Solar Empire. I go home and install it and play some the Tutorials so I can know what I do before I go online. I go to make an account name and password and its says that I need to update my game, so it re-directs me to this website where I have to make an account and provide my CD-Key which is located inside the box. So I do that, and a message pops up saying

"The serial number you have entered does not belong to the email address you have entered. To register this serial number you must use the same email address in which you used to purchase the game."

What should I do? I just bought the game and this is the first time I have ever entered in the CD-Key besides when I tried to while I was attempting to make an account on the game. Did someone still my CD-Key? Or am I forgetting to do something very obvious.