The site keeps telling me my email is already in use
If you are seeing a form like the one below, you may already be signed up:
This form is for signing up to a new account, so it is stopping you from creating a new membership with an email you have already used.
The best course is to login to the site instead. If you have not yet completed the payment portion of signing up, it will walk you through that step before taking you into the site itself.