Right now all the supposedly rice cakes could be anything circular that has been bit. You should add some texture for it to be recognizable (You know, chunks, irregular shapes, rice etc). Google for references and try to apply that onto your picture.
Not sure if you are just going to keep with that palette (I see that light gray a bit pointless, since it is almost unnoticeable unless zooming), but I think you could do an OK rice cake texture with it. (use the two grays you have along with black for depth) You could try going more detailed and start working on dish reflections, etc.
Also the perspective of the dish (or the rice cakes depending on what you want to change) and the sushi are wrong.
There is not much to comment about though, it looks rather rough or unfinished, but good luck with further edits.
