Playing something that other schoolkids will think is cool rather than a bit geeky is something I never mastered. Then again I played oboe all the way through school, you're on sax already. I think you're on to a winner.
Biggest thing for me is to relax. With a wind instrument being tense and on edge screws up your breathing, and I found I couldn't hold notes straight if I was overly anxious, start going all wobbly.
Nerves are good, it's adrenaline, but don't let it overwhelm you. Deep breaths beforehand. Oh, and enjoy yourself
Also, at this time of year silly christmas hats are a must.