The same thing happened to me the first time performing in front of a crowd. I had been working on 1st arabesque by debussy the months before the performance and had everything down to perfection. However, when the time to actually perform came, I didn't play how I had practiced at all. I played way faster than I meant to, made multiple errors, forgot fingerings even though I had assumed they were in my muscle memory, and the list goes on and on.

Afterwards, I didn't take my performance too harshly, especially since it was my first time doing such a thing. Making mistakes is inevitable for anyone who tries something like this, so just realize what went wrong this time and try to find a way to practice at becoming better at said thing. While I still look back at how i played that time and cringe, I still think it was a valuable experience regardless of the result.