I misclicked when doing a review (this one), and that was a terrible goof. Is there a way to fix it?
No, you can't. This is (part of the reason) why a review requires multiple users to look at (except for First Posts / Late Answers, but mistakes there are easy to repair). Those other users will hopefully choose the right action, which will diminish the effects of your mistake. Also, you can always go back to the post and do what's necessary (vote and/or flag).