Calendar -- added a calandar in the side bar every entry.

Not realising that everytime I choose events, todo, etc in a Calandar entry on my MacBook Pro it added another calandar in the side bar. So I changed ALL back to 'calandar', made sure I wasn't going to lose anything from previous months, deleted every other calandar in the side bar except 'calandar', and being about 50 it took some time. Now they're all back. What can I do to delete all these sidebar calandars? Please.