Thank your for post!
You might go to the Records Menu and select "Revert Record...". If you setup Custom Menus that didn't include Revert Record then you may have to resort to a Force Quit instead.
I'm also going to move this thread from the FileMaker Community Feedback Space to the Discussions Space where others might find your post easier and offer further advice.
Thanks for the response. I'm not certain -- this happened some months ago, and with luck I won't repeat the mistake -- but my guess is that menus were grayed and unavailable. If anyone performs the test, I'd be happy to hear the results.