I’m sorry to hear you are having trouble, especially considering the LMS (learning management system) is usually pretty good at loading right.
If it is an account error, as your particular profile isn’t letting you join, then email me firstname.lastname@example.org so that I can manually add you into.
In the meantime try reloading the page, and then load it in another browser (Chrome, Safari, Firefox, Edge, in that order). Allowing for the cookies to be different, and in essence resetting your attempts. 🙂