Well basiically if you look at the (viewers point of~) right finger (of the three, not the back "thumb" one) you see that it has this medium shading, while the middle finger has deep shading on a part that is angled to the light source as the other finger's part that has medium shading. If you would add some medium shading to the middle finger either from the top or from the right side I think your troubles will be gone. But thats just a suggestion though hehe.