heh it helps to place your hands in that position and look at the mirror. I do that all the time when I face that kind of problem.
Here's my two cents:
1) The hand is too small.
2) Have the thumb folded inwards (towards the character's right) to depict a firmer grip on the knife
3) A little more emphasis on the knuckles would help make it better (show a little more bending/angles on the fingers)
Hope this helps.