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Click layer top thumbnail, then repeat the same step as before to cut the ellipse using Pen tool.
We don't need the 3d model layer anymore, so you can hide or delete it now. Still using Pen tool, create the left, inside & right shape (I assume you already know how to use Pen tool). For easier recognition, I suggest using different blue color tone for each shape. Make sure the layers order from top to bottom are like this: layer top, right, inside, left, bottom (see image below for more details).
Now you've done creating the 3D pie, hide or delete the guideline layer since we no longer need it. The next step is adding texture, but first you have to decide where to put the light source. You don't have to draw a polygonal shape to do this step, just visualize in your mind that the light source is from the top right corner (as seen below). Knowing the light source will make your work easier, because you know where to draw shadows and highlights globally.
Open the water image (File > Open). Press Ctrl+A to select all parts of the image, then press Ctrl+C to copy it to clipboard. Get back to 3D pie image and press Ctrl+V to paste the water image. Make sure you place it above the TOP layer and name it wave.
Still on the wave's layer, reduce its size by pressing Ctrl+T (hold the Shift key while dragging the corner control point, this will keep the aspect ratio of the image so it didn't look squeezed or stretched). Hit Enter when you're done transforming. And since we're agreed the light source is come from the upper right corner, we need to flip the wave by using Edit > Transform > Flip Horizontal menu. That's look better!
We need the wave image as a texture for the top shape layer. In order to do that, simply press Ctrl+Alt+G and voila, you've got the clipping mask layer.
Duplicate the wave layer, then drag it down between left and bottom layer. Create a rectangle-like selection using the Rectangular Marquee tool.
Invert the selection by pressing Ctrl+Shift+I then press Delete, this step will erase the selected areas. Now deselect by pressing Ctrl+D. To make sure there is no part of the wave image outside canvas, press Ctrl+A to select all part of the canvas, then go to Image > Crop.