I think you need to enter your game activation code first (which is not the same as the early activation code). I think that the website prompts you for your subscription plan after that. But if you bought a physical copy of the game, and haven't received the game yet, then you'll have to wait for it to arrive before you can enter the code (which comes with the game). A lot of people (including me) are in this boat and won't be able to play the game until our copy arrives.
If you got your pre-order from Gamefly you might need to go to their website to collect your key. They didn't send me mine in an email, I just happened to go to the website and find it.