I`m not conversant with this kit or the components but I picked up the following trick some years ago and it makes this job a breeze.

If scratchbuilding, plane these items to the wedge shape with a razor plane from the full sheet of balsa. Cut the ailerons and elevators to width from the full sheet after the planing is done.

It really makes the job a lot easier than struggling with shaping these items previously cut to required planform.

Alan W