Clean and refine the bezel sides by sanding first with 320 grit sandpaper. Repeat with 400, 600, 1200 and finally 2000 grit sandpaper. Hint: Use an ultra fine point Sharpie marker to mark the washer to help know where to start and stop sanding. Remove it with an alcohol soaked pad.
Place the bezel, washer facing up, on a piece of 320 grit sandpaper. Using two or three fingers to hold the bezel down, use a figure 8 motion to sand the back perfectly flat. This may not take much as the rings were already flat.