deleting flagged mailboxes in Mail app

Hi, So I have a bunch of Flag Mailboxes which appear with the numbers by their side saying how many flagged emails exist in that mailbox. Thing is I accidentally deleted ALL of my mail from my mailbox from the original server (gmail) and can nolonger retrieve them. In the Mail app, when i click on the flag mailbox, it is empty (as they have been deleted off the server). However it is still registering as having flagged msgs in them becuase I was never able to get in there and unflag them.

Is there any way at all to delete these flag mailboxes? I've tried closing the app and opening again, restarting, checking my gmail to see if they are indeed deleted (they are). But nothing has worked so far.

Cheers

Sarah