Ah, competitions. I remember fondly my early days of dance, listening to a muffled announcer, with a costume with enough sequins to coat a rather large disco ball, waiting anxiously in the wings as teachers coached, a scarce audience comprised mainly of parents and dancers cheered, and judges judged.
First of all, congratulations on making your "Teen Jazz Line" competition class. Competitions are a great way to get used to dancing on stage and preparing for a performance. In fact, many of the SYTYCD dancers got their start through competitions, and my old dance teacher used to tell us endless stories about when she "saw Tyse D'Orio at a competition, but his real name is Keith, and he won this and that..." Personally, competitions were a major growing experience for me.
Yes, you do get nervous. Depending on what kind of a person you are, you could be calm and cool, or you could be extremely nervous. I had a friend that was a wreck in the wings every time before her solo, but when the lights were on her and the music hit she was fantastic. Basically, if you are nervous, take that energy and fuel it into your dance. And to prevent major mistakes in your dance, go over it backstage or in a hallway thoroughly before going onstage. If you know your steps, chances are you won't mess up too badly. And the beauty of competition is that there's always another coming up, so even if you mess up you always get a second or third chance and expirience.
Are they fun? You bet! One of my clearest and happiest memories from dance competitions is when I was in a Junior Tap Small Group, we were all about 10 and there were 7 of us, and our tap number was one of the strongest in our school. Everyone knew their part, so we all played off of each other and had tons of fun on stage. To make things better, this dance got to the competition's "dance-off" (some comps have this thing where you take the top 3 numbers from each school and have them all dance a second time, and the highest score gest a humongous trophy.) Low and behold, we won the highest award of the whole competition. We beat out lines, productions, you name it. It was great (all we could say was "Oh My God" for about ten minutes!) The combination of the fierceness of competition, the glamour of the stage, and the fun of dancing make for a lovely experience that is extremely fun, even if you don't walk away with a trophy twice your height.
Bottom line, dance competitions are an exciting and fun way to grow and develop as a dancer and performer. I'm sure you'll have a great time performing and competing with your friends, even if you get a bit nervous. Best of luck!