Create a new layer and mark out a certain zone with Rectangular Marquee Tool (M), using also the shown brush before of white color just to accentuate the right edge:

Make a copy of this layer, reflecting it as in the mirror with Free Transform option. Apply now the Burn Tool (O) to dark out the border of the original layer.

Apply the same kind of processing on the horizontal position.

Using the Burn Tool (O), dark out the mirror – copy: