If you were in the process of registering an account (on desktop or web) and didn't complete your registration, you have no 2-factor authentication configured. Thus, you will not be able to log in.
To remedy this, simply click the original link you were sent in your registration email. Either from when someone invited you or when you received an email to confirm your email address.
You should promptly be taken to the correct stage in the sign-up-process, and able to complete the form.