All functions and use cases would be too expensive to test, keep to the main process of logging in and test it once
Look at your website and emails on a smartphone, 20-30% of the participants see your page only
Also send invitations to your orga team, more eyes see more
Show your web page to an unprepared colleague for 5 seconds and ask him what it is about. Some participants only invest so much time in their pages and should still know what to do
Do not force your participants to think - every step and question should be self-explanatory. Now give your colleague enough time to get around and let him say aloud what he thinks. Maybe he can give you a valuable clue.