What if I'm not the best at my main EC

Basically what the titles says. I’m applying to several competitive schools Cornell, Vanderbilt, Brown etc.this fall. My main ec and the biggest part of my application is band, and the topic of my essay is going to be my experiences playing my instrument. The problem is I don’t feel like i’m especially good at my instrument (and my accomplishments don’t back me up either) especially compared to the caliber of students applying to these universities. I’m wondering if having just a small level in my main ec will be detrimental when applying to these colleges. After all I’m not even first chair in concert band. I am a section leader in the marching band though which does help.