First off, congrats on putting together your first piece! That's a major accomplishment!
I liked how you moved between time signatures and keys - really helped keep track of where we are in the story. The way you phrased the melody was also nice to hear.
The main feedback I have for you is that I would've liked to have heard a little more variation in the dynamics. Not necessarily the overall volume, but more so the intensity of the notes being played. For your next piece, try to incorporate dynamic markings in your score, so that the instruments play softer or louder depending on the tone you're setting for a particular section. IMO, this will have a greater impact than just lowering/raising the volume and still playing the instrument with the same intensity.
But please take this with a grain of salt. What you did for your first piece was awesome, and the fact you went for the hard mode on your first attempt is impressive.
I can't wait to hear what you do next. Keep up the good work :)