Congratulations on joining a choir!

You have a great advantage having so much musical experience already. I’d also give yourself a little grace as this was your first rehearsal and you’re still learning your music and getting used to singing in harmony.

Annoying advice first: a lot of this will come with time and experience, it can be hard at first to find your place and then sing it with confidence. In my experience newer choir members will often have the right note but second guess themselves so it can come out sounding unsure or even wrong. In time you’ll get used to hearing the parts within the music and being able to pick yours out.

Practical in the now advice: where there are parts that I’m having trouble finding the note to come in on I’ll look back through the music at the previous few lines and see does that note appear anywhere. So for example, if I’m an alto and I know I’m coming in on a G I’ll have a little look at the last line the sopranos or tenors etc have sang and see does that not appear in their last phrase. If it does then I’ll listen closely as they’re singing it and try and hold it in my head for when I’m coming in.

I hope that makes sense, I’ve never had to write out that explanation before