Take another small piece of plywood. Put a slot in it that the cord will barely fit in, maybe an inch or so deep. Slide the cord into the slot and position the plywood so the cord is against the side of the hole you drilled. Screw it into place, maybe positioning your hole through the plywood so you can screw this other piece of wood into a stud or something solid. If you ever need to remove the cord, use reverse on your screwdriver.