Didn't realize how short of a source you were working with. My first comment would be that you did a pretty good job of taking about 20 seconds of music and stretching it out to three and a half minutes without coming off as too repetitive.
But it is a little bit repetitive. By varying up instruments you eliminated a lot of it... still, there are some spots where I think it could stand to become more noticeably varied. Like at 1:15, after the cymbal fill/transition you introduce the bass doing its thing, but it's not coming through strongly enough. The bass either needs to be louder or have more "presence" (well, I mean, it should be producing sound in a little higher frequencies so I can hear it) or both.. maybe some messing with the EQ, a new bass sound, or maybe taking it up an octave would take care of it? It's part of the mastering process, I guess, and it's somethin I'm not great with either. The bass is more noticeable in the un-eq'd version, so just keep tinkering with it till you get a good sound.
Takes time.. lots of time. Which, with youth, you might have They say youth is wasted on the young, so... don't let it be wasted. I'm not old but I sure as hell wasted away most of my teens (last one to go - hopin to make it more productive, lol).