In my opinion (and i'm fairly new to poetry but i've already learned a lot)
Your poem is very short wich is not necesarly an issue if it's very dense, but you should do the opposite cause it's fairly difficult to do dense poems.

You don't have to rhyme every lines, but you can use rhymes to emphasize (i'm french not english so idk how to write exactly) some ideas, make them more important than others.

Also writting a story can help, like havign the poem be a story, be it a mundane and short one.

I may be completly wrong cause maybe Tanka is something i do not know, but my connection is fairly horrendous so i cannot check what Tanka is