Domain mapped, now I can't log in

I mapped a domain using domain mapping - not sure which setting I chose. However, now I can't get in to the /wp-admin. When I try, it does this

http://site.com/?__domainmap_action=domainmap-logout-user

How do I fix this? Is there a way to undo the domain mapping and start again - I can't figure out how to fix it if I can't get in.