Hi Maxx,
I think your musical ideas are pretty good, especially for just a high school senior. I've scanned over what most of the previous posts said and agree with all of the points. Besides working with elaborating on your materials the biggest thing you need to work on is:
working with your samples.
While your samples don't sound bad, you need to use them in only the strongest, most realistic way. Some of your short attacks sound very, very fake. Here is how to fix that:
1) First off, select the best sample in your library for the style and attack you need. If this means having to use multiple string samples over the course of the piece, then do it. The end result will be much stronger.
2) Write out the passage and then start editing the velocities. Right now your velocities seem very monotone. This is especially true in the snare drum part. Go through each line and imagine, research or study how the actual instrument and musician would behave playing that line. Does it crescendo, decrescendo or have a strong attack and then back off? Also put in accents this way. Provided that you're using multi-layered samples (which most East West stuff is) you will be able to breath new life into this piece.
As far as the length, yes it is short but sometimes that is what is needed. In my full time job, most of the music I write has to fit within 30 to 60 seconds for TV restrictions. Occasionally, I get to write a longer piece but those are usually the limits placed on me. I think you've done a fine job getting started here.
I'd also consider bringing down the snare drum part and tweaking the reverb. Remember, percussive parts will always cut through the ensemble sound more because they are usually shorter attacks. There isn't a need to have them at the same level as the ensemble. You want it to embellish the ensemble sound, not attempt to over take it.

"The Snares are coming!"
I really like the slow(er) section in the middle.