The back of the left and right side of the jaw looks like they're too high and a bit too wide. It might help to imagine the face without the mask or look into the mirror with the same perspective. On the other hand, I don't know what to make of the mask. If the mask is made of hard material, then my suggestions don't really apply. But, if it's soft material, then the mask would be form fitting. I hope this helps a little.
Thanks for your suggestion.
I've tried to make the mask more like a metal helmet, but you're right the jaw looks too wide.