I should add: in order to a person to see themselves - the surface needs to be very flat horizontal. Even when stretched tight on my spaceship, very small natural ripples in the plane of the horizontal - made it 'reflective' but only of scattered light, not an real image.
Make sense? Hard to explain. Anyway the plywood backing would have to be super flat on planer then curved in a wavy way up and down...the pre-made mirror being of a single sheet of thicker plastic, can create this surface need for a image reflection.