Yeah the size is too big, I myself have tried doing a piece 320x240 (not saying yours is that size) size range, and it took me a lot more work since the areas are too big. I say 100x100-120x120 would be fine to resize it to and work from there. Now, as far as the shading goes, the problem I see is that there is no definite light source. Like in the eyelid it's shaded darker, when it should have no shading.