If you are playing in a marching band, the most important characteristics of your alto are reliability and ruggedness.  Make no mistake, your sax will take a beating in marching band.

Good construction will trump tone in the marching band, because no one in the stands will here anyone's individual tone.  For this reason, I would go to a reputable second hand dealer and look for a well refurbished Yamaha YAS-23 or similar horn.  They even have some on this site.

If you are also majoring in music, then you will want a better playing horn for the remainder of the year.  But you do not state that, so I will not approach that topic at this time.

Good luck and have lot's of fun! (Oh, and consider a synthetic reed, you do not have to keep it moist, and it won't easily break when you stumble or get bumped into by a trombone player.)