Morning Tom. Apologies for the confusion. Some of the pieces have changed slightly from the initial plans version to the kit version. Tweaks have been made for economy of wood or ease of installation (as with the hatch surrounds). I've put it on the to-do list to modify the kit-supplied plans to reflect these changes.
I believe the revised curvature (the one on your pieces) more closely reflects the curvature of the deck. It's a tricky shape to achieve perfect contact because it ends up being two curves coming together, therefore any variation in either of the two curves can make a big difference in position. If there are gaps, it's not a problem, as both sides get filled with epoxy fillets, so any holes or gaps will be filled with epoxy and sanded..