jUST A WORD OF ENCOURAGEMENT:
I think it needs be said that a lot of production dinghys use centerboards - literally. they round the frontand rear edge. Yet without the board, the boat simply will not sail upwind. Cats with some weight on (leeward hull) board to make the hulls bite, can sail poorly upwind without boards. Chrysler made a cat with board boards. (no foil shape) One presumed it sailed.
Point is, however badly built,whatever the profile, if it is strong enough it will work OK.
A bunch of 3/32 plywood glued together makes a "contour map" as the glue lines expose as you sand. By eye, you will do a nice looking job.
Cutting a profile out of plywood and using it to check as you sand, will get you right on.
Two layers of 6 oz and you should be strong enough. The lateral force will be about 200 lb so if you laid your boat on its side and cn stand on the tip of your newly made board, it should be plenty strong enough. Or support the board by a brick under each end, and two of you stand in the middle....