If you didn’t cut both the top and bottom boards at the same time, make sure you trace the baseboard onto the top board piece, and made the cuts as well. That way you’ll end up with two identical pieces.

Here’s what the final cutout base should look like. I used 2 full sheets of birch hardwood, but you could save some money and use a cheaper plywood if you like (especially if you’re not doing a racetrack).