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It says that for me, too. I tried to click the login since I just FINALLY got my email.
It's just because they're doing updates and tweaking things and whatnot. There isn't a place you can check your account, you just have to be patient. Remember, Pottermore is still really new.
Have you ever heard of Neopets? Did you play in the early 2000s? If you did, just remember how often the site was down, because it was new.
Their servers are probably overcapacity right now, and they have to fix some things in order for the number of people that have an account to play all at once.