To cut the other part of the joint, make a spacer stick to move the router toward the front of the jig board. The spacer stick needs to be the size of the router cutter. It can be worth having slightly different thicknesses to allow joint fit adjustment. Replace the practice pieces so...
Use the hand plane to shave off material where the top needs to be lowered. Make sure to go against the grain to avoid tear-out as much as possible. After you’ve flattened the surface, smooth it out with a hand sander. If you don’t have a hand plane, a belt sander will work,...