Hi sticher,
Thanks for posting your question. I'm more than happy to assist you. There's a few different ways to log into the Premium Website Builder. You can log into builder through AMP. On the account and billing details page, under the active subscriptions you will see a login link.
Also, we have a tutorial on how to login:
How to login to Premium Website Builder
If you need further assistance please feel free to contact us.
Thanks!
Tim S