HackWilson1930: Can't just accept the invitation to join a CC if you are already a member of another club.
Bare of experience, I doubt that. If you can receive an invitation while a member of a different CC, it should work out (I have heard (*)).
BTW: The QUIT button (on PC) is on the homepage of your CC, not too far below the top (again, I was told (*))
(*) some features are out of reach for CC owners ;)