I’m assuming you have clicked here:
When you should have clicked here:
In other words, you have created a student account for the classroom edition instead of starting the campaign mode.
I believe you can delete your account and create a new one, or ask @nick to have your account de-studented. In any case, you are still able to play the campaign mode by visiting this link.
If I recall correctly, @nick mentioned they would improve the separation between the classroom edition and the “legacy” mode, perhaps creating separate homepages for each. I don’t know whether there has been any progress in this part.