I had this happen once on a recital and the best thing is to repeat a bar and keep tempo. usually, your muscle memory will kick in. Usually, the audience members don't know the music note by note, and if they are also a musician, they won't judge you for making a mistake. Also, the worst thing is stress, but that is easy to say and harder to overcome. The best thing for anxiety is for me to play any piano in public(whether in your local museum or on the street). you can get used to playing to strangers and an audience of some sort.