Congratulations! I get pretty nervous before showcases and competitions. Here are some things that help me:
-- do a rehearsal of all my dances in my costume, hair, and make-up beforehand, so I know there won't be any "wardrobe malfunctions" and I know how to get the look I want without having to experiment the day of the performance
-- rehearse my dances in the order I'll do them at the event
-- don't expect perfection. Everybody makes mistakes, even top pros. The goal is not to make no mistakes, but to know how to not react to them visibly and how to recover from them fast. I do as many rehearsals as I can that go all the way through the dance no matter what happens, so I can practice recovering from mistakes.
-- try to remember it's a performance, not a test. The more you can enjoy dancing in the moment, the better it will look to those watching.
-- remember the audience is on your side. They know what to expect from a beginner and they want to see you do well. (By the way, you might find out whether it's customary for spectators to cheer at your studio's showcases. The first time someone yelled my name during a showcase, I was so startled I looked over at them and totally lost my place.)
-- I don't watch the other dancers before I dance. It does cut down on the fun of seeing your friends perform, but if I watch, I tend to start comparing myself with other dancers and get more nervous. That's just me, not eveyone feels that way.
Good luck! Let us know how it goes.