thats a great shot, I am struggling too with this shot, first time i tried it was so bad, but i will try again too! glad you tried, its a great result with nice colors
you're shooting with a 36MP D800, so feel free to back up a little (double your subject distance), then crop down. the closer you get, the more your DOF decreases, exponentially. even f/51 wouldn't cut this shot at 1 foot with my 105mm macro lens. also, moving your flash closer increases your light exponentially as well. fire the flash horizontally and put a white card opposite the flash to reclaim some of that light.