Well.
1. It's not finished. That makes all the colouring invalid, as the white spaces stick out like an Alec in a pedicure salon.
2. As you said, the outline is thick. Way thick.
3. Try doing it like this, next time: Before going into details, shading and stuff like that, fill up all the empty spaces with a "Base Color", the average color of the thing you're painting, so you don't have ugly white spaces like that.
4. After doing a layer of said base color, make a layer for shadows, another one for highlights, and flesh out the details.