Those laminations are a big step. About the 1/8" springback; I would cut the sides as it is, and not worry about the 1/8" on the inside. You will just have less to cut back for the inwale, and the boat's scantlings are extremely robust; nothing will be measurably weaker. If you use a cross piece to pull it in, then the frame may force the sheer plank out of a fair curve when you remove the piece. Maybe not though; 3/8 is pretty thick, and quite stiff. The other dimension is probably no problem either, but you should be aware that the centerboard trunk stops right at the forward face of the frame. It shouldn't matter, though.
In other words, i don't think you need to sweat either issue too much. All the same, if you side the frame as shown on the plans, you will find extremely strong.
Other, more professional voices will probably chime in. Full speed ahead!