play the violin better

I’ve been playing since I was in 5th grade, and I had gotten better through 6th and 7th grade. But this year, I became part of second violin, which really isn’t that bad, but I miss playing melody, and even when I try hard I still could not make it to first violin for the last concert. There were originally 7 second violins and I would always be first or second chair. Now there are only four, but I’m still first chair. There were originally 5 firsts, now there are 8. I really don’t understand why I can’t get first violin, when I always get first chair on normal playing test. But when it comes to first violin auditions, I get nervous. Can someone please give me tips to help me with auditioning, because next year I need to audition for the orchestra, and I want to get into Concert Orchestra, which is one higher from the lower orchestra (Cavalier Orchestra) and one lower from the highest orchestra (Chamber Orchestra).