I think what you have so far is lacking volume (as has been pointed out) and looks messy. Lots of, what seem to be, random pixels going on in the stomach area.
Not sure if you wanted a straight on view or slightly top down but right now it looks fairly straight on while the shadow suggests a bit more top down then is shown now.
Colors are also a bit boring. Try mixing it up and adding some other hues/tints in there.
Did an edit which is mostly a recolor of the lines to show you some ideas. Hope it helps.