I think this has been hinted at in previous replies, but I will say it again: as the melodic content of the music is intentionally limited to just one interval, you need to expand the other parameters in order to generate the necessary sense of development. Particularly so with rhythm: I think a more innovative palate of rhythmic devices would bring this from being a promising piece to being a good piece. The lack of contrast in m. 7-14 is one example of a place where the music becomes static due to circling round the same pitches with no rhythmic development. Also, the near-verbatim copy+paste of the opening section seemed to me rather lazy and was something of an anti-climax. It needs a more intense way to finish.
Technically little of concern. The open D at 79-84 could mask the upper register notes, but a good player will be able to control this.