This creatures must be the weakest of the D&D universe! Your concept is a lot more stylized and simple. I like it but try to make it bigger and make some shadeing in it. If you want to make it like the original, you should put this big folds in it and and make the hands and foots more flat and longer.
honestly, i don't think the shading matters all the much. i'd use the original concept image you're using as reference for form information and create an ortho to help lay down the geometry and get more familiar with the creature. i would however suggest you either draw bigger, use a sharper pencil, and work cleaner and…