Learning keys on the piano and confidence in singing

This year I’ve been learning how to play keys on the piano and possibly accompany myself. Although it’s a slow process I’ve been working hard to be independent in learning music. I’ve also learn this year how when I’m practicing by myself my breath management and rhythm is really good. But when I perform in front of others my key is off or my rhythm or I’m short in breath. It’s very confusing on why I can perform so well alone, but around others I’m only subpar. I hope that next year I will be able to not only accompany myself but be able to find my confidence in perform in front of others again.