It's cool to see devs branching out into music - I think for no prior experience this was a good submission.
If you plan on continuing making your own music I'd suggest looking into writing variations on a theme. Since you've established a few melodic ideas in each of your tracks I think finding ways to make small changes to them (either in the melody itself, the underlying harmony, etc.) will add a nice bit of variety in the music and help you further develop the ideas you've already got.
Thanks for sharing this, and keep up the good work :)