Cut a piece of 3/4" plywood to the size of your headboard. Miter cut the 1x2s to fit across the top and two sides of the plywood. Screw or nail the 1x2s to the sides of the plywood. If you don’t have a saw, ask the hardware store to cut it for you.
Lay out the pattern to determine spacing in between each piece of cardstock. Adhere the cardstock to the headboard using double-sided laminate flooring tape; it’s available at most hardware stores. This tape is very durable and will prevent the cards from moving or bending. Lay the tape on the plywood in evenly spaced rows.