In your account, follow the "Code Redemption" link. It should mention when you preorder code was entered.
That code is the one that was first sent to you, to guarantee Early Access.
When the game is officially released (it's not out yet), you will receive another code, your serial code, that will be usable on the official launch date, the 20th of December.
The code that is asked on the main account page is the second one I mentioned, the serial code. So do not worry for now.