I don't know how else to learn this song,

I (16m) am taking voice lab in school, (I don't know if this is what every school calls it, so I'm just going to assume its not, sorry if I like mansplain) basically we kind of run it in a way, every class we go through a cycle and war up the rest of the class. Our teacher picks a song for us and we learn it as a class, then do a trio run through, then a solo "push through run" without comments from classmates, then solo with music and comments from peers, them memorized with comments, then a recorded memorized run. Our teacher choose Vaga Luna Che Inargentis, by Vinchenzo Bellini. Outside of class I have listened to multiple reference recordings dozens of times and hummed or sung along with them and have taken a few hours of dedicated practice time for it. I've used a piano and plunked parts out to get better with them. I went and asked my teacher "Can I run through the song with you?" and he told me "no", this was before today).

Today I had my push through run, I got through my slate alright and my teacher started playing the piano accompaniment that starts before I come in, and I just fell off, I couldn't get my starting pitch right, he literally had to play the note for me to get it, I was probably off pitch the entire song, he had to adjust his playing like six times because of me, and my right hand was shaking so bad I literally had to grab it to try and stop it from shaking. I got through it, but it was awful. I've never done this bad with any song before, even ones with less practice.

I feel like I'm just embracing myself in front of everyone (same thing happened when I was doing warm ups the other day) and wasting their time, I don't know what to do with this song, I just don't want it to happen again, what are some things I should try.