The top seems a bit too light
I think you're right. I was trying to separate it from the edges of the gem, so as to give it a little more of a cut look, but it winds up looking like it sticks out a little. Maybe toning the green down in the middle will help.
The gem looks nice. I think the highlight in the center is unnecessary though. It makes it look like that the inner lighter shape is protruding straight out. Maybe it's just me.
Oooh love that shiney!