First of all, sorry for the extremely delayed reply (four months!). I simply could not find the time and motivation to compose. Of course, I am still very busy right now, with college admission and AP test preparations. I will be finished in a couple of weeks, however, and I hope to finally get back to composing. I might actually go for a Composition minor, if that's allowed by the Computer Science department.
Secondly, thank you for all your comments and suggestions. I will take all of them to heart. I'm now almost done my first real Music Theory class (high school AP Music Theory), and looking back at this piece, I see a lot of places that can be fixed.
@Rafn: You are right, I don't really have a theme present. The simple left hand pattern was more of a "safety feature," if you will, of my novice self. Now that I know more about music theory, I will attempt to modify the LH a bit.
@aerlinndan: I do not know why I did a four-measured intro. I now realize that my ears had always yearned for the intro to end after measure two.
When I wrote this, I did not even realize that P5's were "illegal." I'll do what you suggested. As for the vii, IV, vii, I will look for a more powerful progression.
The lack of a modulation was partly done on purpose, but I have no good reason of why I did that. I suppose I was just trying things out. I'll see what I can do with this.
I also don't know why I did not end with a root chord; probably lack of music theory training. Actually, it was to make the hand movement easier and to contrast with the right hand movement, but I will rethink that ending.