Ok sometimes its easier to just draw it by hand....saves you a lot of time and "trying out in vain"
The way I would do it is following steps;
1. create a fore- & background layer....ie. separate the colors. so the lighter gray would be the background, darker gray the foreground.
2. create a shadow layer above "Dark Gray layer" (top layer) use a darker version of the Dark Gray you already used and trace where you want the shadow. Turn the opacity down on the "Shadow layer" to around 45%, and use the smudge tool to blur the shadow into place.....
3. Make the shadow layer a Clipping mask onto the Dark Gray layer by pressing (Alt + Click between layers or Control Click for MAC)...this should hold it in place only on the inside of the apple.
4. Repeat #2 & #3 for the highlights, except that you would clip the highlights to the light gray layer.....viola, should do it.
hope that was helpful, it's just an alternative to Bevel & Emboss really.
I'll try to upload a Tutorial with Pictures later, but I'm at work right now

...oopsie.