this is something you can ask your music teacher too. i was in a similar situation. especially for jazz big band. i was good in middle school, then in high school i started in the lowest band level, and only got to the highest in junior and senior year, but i had to switch from alto my main to tenor, because there were other alto players better than me.
that's just the way it goes. it's not anything you're doing wrong, it's just the director wants the strongest members in their bands to sound the best. first char isn't always everything, sure they may get the melody all the time, or maybe some solos, but without the other chair positions, you don't get those cool harmony sounds. sure i would have loved to play first alto, but when i was 2nd Tenor, i got some cool parts that included me learning how to double on flute, and on soprano sax as well. and in that chart, i even got a solo and another soli with a trumpet player as well.