While as you said yourself the sketch isn't perfect - it's not bad Lantist, you have the potential - just gotta keep practicing :)
The proportions are almost all there - perhaps her legs, which it seems you've shortened to get on the page make her seem slightly off balance. Also her hair - her fringe looks a little stiff - though perhaps that is the design. I just like seeing smoother/flowy lines when it comes to hair.
I love her design though :) Keep it up :D