The shape of the tubes in the illustration gives it a bulging outward look, while the shape you created makes it look like the tubes are going straight down.
I feel the center of the belly with the tubes is actually more spherical and recesses into the body instead of flat like you have it. A spherical shape is also much more interesting than just being flat. I feel the shoulders and head need to be bigger as well. Don't rely on overlaying your model trying to match the concept…