You have no lows, only highs and mids.
You need to bring some 6th graders with you to UIL. Teach your ass off and get it done. You need a tuba player, or at least a bass clarinet and let a percussionist hold a tuba in the back and fake it.
A smart flute player can learn and play tuba really well.
School of thought 2:
Go and do your best with incomplete instrumentation and get a 3. /shrug. who cares anyway?
School of thought 3:
Dance Celebration - easy you don't need much lows here, put the tenor player on bass clarinet.
Rose hill march - 32 bars long I think. Pure cake and doesn't take much
Ming Court? Mystery Ride? Sakura? All of these can work for you
My opinion: Don't go, do right by the kids and teach as best you can. Resign before NR.