The only thing that's really jumping out at me is that the legs look a little too short.  A good anatomical guideline to keep in mind is that the crotch should be quite close to being the midpoint of an adult's body.  That means that a person's legs should be approximately as long as the rest of the body, including the head. 

Another thing is that the torso looks a bit stubby to me, at least compared to your reference.  I feel like you could slim down the waist a tad.  However, this might just be an illusion caused by short legs, so I'm not sure...

The pose in your piece came out looking stiffer than the pose in your reference, although to be honest it's hard for me to figure out what would fix that.  The only thing I'm seeing is that in the reference, the foot in the left is uprooting from the ground somewhat, whereas in your piece it (appears to be) flat on the ground.  Also, take note of the fact that in the ref the foot is pretty close to facing the viewer, whereas inyour piece so far it looks like it's facing in the opposite direction of the other foot.  However, I might just be misinterpreting your sketch.

Good luck. : )

I don't agreed with showtime... I think it looks fine and I'm looking forward to see it finished :D