I'm a second Tenor and I need help learning how to become a first tenor.?

I'm in an original adaptation of Aladdin at Junior University Musical Theater. In the show there is a worshiper who sings this first tenor solo... I am not a first tenor, I'm a second tenor, there is no way I can hit those high notes. So anyways, they were having auditions for the Worshiper, and I don't know why I auditioned for that part, but I did. When I got the music, I almost fainted because there was no way that I was going to be able to hit those high notes..So when I was lined up with everyone else I was pretty nervous. When I got up there to sing the song I nailed it, and got the part. But I've never been able to hit those notes again, and now I'm pretty nervous b/c we have rehearsal for my solo tomorrow night. What should I do to bring out this hidden higher-range not that I didn't know I had?