This is only my opinion...so take it for that...just one person's opinion. I'd change the seat color to make it very dark...almost black so that the entire lizard would pop more off the page....just to draw even more attention to the lizard & not the bright seat of the chair...because that's what my eye is drawn to first. Add brighter highlights to the girl's cheek, chin, nose, and lips. Darken the shadows on the hand holding the lizard. And finally add a bit of pinpoint colored highlights on a few of the lizard's scales. After that I'd see where it is & if it needed any more drama or sparkle.
It's a cool concept...this soft delicate looking girl holding this giant scaly lizard in a melancholy setting. You've got a great imagination & the proportions look great! Keep it up~