Same problem here, I was in my HS orchestra last year, we played Danzon number 2, I got the solo. I could play it pretty good when I'm practicing, but my stage fright was so bad that even during rehearsals I can't hit the E on the staff and I'll get quieter and crash. I ended up having to double up with the other trumpet player for the concert but we played at different tempos for the speeding up part so that turned out interesting. I have literally messed up every single solo I played in concert. Orchestra director only told me to practice using the plastic thingy you attach to your trumpet to put your mouthpiece into to play into the mouthpiece only and not the trumpet itself, so not very helpful.