It's one thing to have a great Voice, but learning how to perform on stage requires a whole new set of skills.
When singing on stage, you're not only combining language and music, but you also have to deal with spatial awareness and be aware of the people around you. Watch the conductor if there's one. Enjoy the feeling of being on stage. Look around you in rehearsals so as to get used to the size of the performance space and think of how much energy you will need to fill that space. Also do well to ensure that the energy of a piece of music is conveyed in your singing.
Note that everytime you perform, the atmosphere in the concert hall is different, the people watching you are not the same.
Being a major cast in a concert is a wonderful experience, but it's also a big responsibility because you want to prove and feel reliable. Overpractising should be avoided.
Stage fright is what can happen to anyone, professional or amateur, but i tell you, you can slay on that stage through your singing. Imagine the concert hall being empty or imagine the audience in their underwears (lol), and just relax and calm your nerves. By the time you sing your first line, i bet you, you'll feel alot better.
The stage is like the home of a singer/soloist. Relax and feel free on stage the same way you do in your residence.
I hope this helps you overcome that fright...
You Can!!!!!