Ah yes, I remember those things! I never took part in any of them.
I could suggest: modulating, varying the counterpoint, and perhaps a little development on the main theme. Also less repetition and more harmonic content. You can add some chords in some of the phrases that you repeat, increase rhythmic contrast... Actually I can edit your file if you don't mind. In this form it's a bit boring, I'll have to admit, but for a school party it's very fitting. That's what your teachers would expect you to do I suppose.
Of course I don't know how capable your friends are, so maybe this is all you can do with the available material.
