Intro's very nice. The only thing I dislike is the marimba part. It's overkill to have all those rolls. Maybe change that to a single hit, or remove it entirely?
Nice chorale writing following that.
At C it's very nice, but the melody's getting a bit repetitive. Variation in harmony scoring will fix that.
At D I don't really care for your string writing. It's too much like hanon for the piano.
I LOVE the flute/oboe duet at E except for a few things. Keep your unisons to a minimum, first of all. The support of the oboe is a bit weak in unison with a flute. I'm posting a graphic of a harmony I liked, but feel free to edit ^_^
I would work on the harmony in the following section at F too. It's a bit boring.
At G the marimba is annoying me. You need steady support, not jiggling rolls :p
All in all very good for a first piece though
congratulations
What school are you performing this at? I'll come if it's nearby
I'm from michigan too.