I'm the best pianist in my district and can confirm that this still happens

this is very relatable
you just gotta relax and just remember what you can do at home

I've been a concert pianist for 6 as a half years and a bassoonist for 3, and these slip-ups just randomly happen, like during a solo and ensemble performance on piano I forgot what I was supposed to play

AAHHHH I MESSED UP DURING MY SOLO ;-;

Yeah I feel that
I have three or four solos in my marching show last year, so I'm not stranger to mess-ups in solos

marching band = best form of band

Yes
Front ensemble pianist for the win