I get the sense that you're new at this, so I hope you're not offended if I offer some advice. What you have there is an opening riff or theme that's good for 15 - 20 seconds, maybe 30, and after that you need to be introducing some new textures, rhythms, instruments, counter themes or other elements to add interest. You may want to check out some of Blipp's song posts. He is a master of developing thematic material.
Hope this helps and that you'll keep plugging away at it. It takes time.