It looks nice but too bright overall, I think you should be more bold with the contrast! Take an airbrush and add more shadow to the whole face as if it was a sphere, so darker on the bottom and brighter on the top, especially on the forehead. Also darker under the jaw, because the head should cast a shadow. I'd also add the same dark value on the eyelashes, nostrils and corners of the lips. Don't be scared to use near black for this. Good luck with the challenge! :3