Lay the plywood panel flat on a work surface. Orient the board horizontally, lengthwise. Select one 96-inch side at the top of the headboard.
Form the flexible curve ruler into a graceful, aesthetically appealing curve along the top edge of the headboard. Experiment with different curves until you are satisfied with the overall appearance of the curve.
Trace along the flexible curve ruler with a pencil to transfer the curve to the top edge of the headboard. Set the flexible curve ruler aside.
Place a jig saw flat at one 48-inch side of the top edge of the panel. Align the blade with the outside edge of the pencil mark. Guide the saw along the pencil line, moving just fast enough to allow the blade to cut through the plywood until the cut is complete.
Sand the cut edge with a detail sander equipped with a fine-grit pad. Move the sander along the curved edge in a smooth motion, allowing the sander to do the work without pressing it too hard against the surface. Continue sanding until the cut edge is completely smooth.