Sometimes complicated board shapes don't get translated from 2D to 3D. You'll probably see an error that looks like this: 

As long as your board looks solid on the 2D PCB, we it should be fine. ("Solid" means that the inside of the board is black, and the outside of the board is grey.)

Skip the "Push to 3D" portion of the instructions, and use the Cam Processor tool on the Manufacturing tab of your 2D PCB view.