You're right, it's complete as it is; and it expresses a lot in not many words. Rhythm and rhyme don't really do a lot for pieces as short as that, as they develop power over the length of a poem (and after enough length, drive you crazy). The opening assonance is very good.

The difficulty is in making what you do well work well over longer works, where the rhythm and rhyme keep the stress evident, and give power to assonance and alliteration that does not emerge nearly so easily without the rhythm and the rhyme. But I'd really like to see you do that; your imagery is good. Sprung metre would be a very good starting point.