The strength of that seam comes not from fitting the wooden panels together tightly, but from the filleting. And overall strength comes from the glassing overall of the hull. The better you do your cut outs, the less gap of course you will have. However, not only must you cut accurately on the line you've drawn out, but that line, and the line on the other panel, must be correct. This is not always the case, particularly if you use a template, especially if that template comes from CLC. I would be embarassed to send out a template as bad as theirs is. Even using offset tables and battens, you will still find variations and inconsistencies.

Easiest way I know of to bevel the edges for stitching is to use a small hand plane. Takes about 10 minutes to shape all the panels for the entire boat. This isn't rocket science, so you don't need perfection. Just eyeballing how much bevel to give various areas works just fine, and results in a smooth flowing transition, which is vital. Trying to stick a file or sand paper between pieces as you're stitching them will result in inconsistencies. Giving problems with symetry across the hull, and problems with panel alignment along a seam. Not to mention the problems of trying to stick the file or sand paper through the areas that are already wired.

About the easiest way I found to stitch panels together is to very losely join them, and work towards tighter. Starting with the bilge panel, and the lower two panels. Joining them very losely amidships, then bringing them up partway with some end stitching. Working tighter, centering the panels (which means snipping wires), filling the stitching, and building up the shape. Repeat as you go up. This allowed me to completely stitch my final hull (round two, because of lots of problems with panel shapes on round one) in a few hours. A rather bloody process btw, as you tend to stick yourself with the wires, especially if you are using fine wire.

It is probably more important to be symetrical then to have an individual seam correct. If the boat is symetrical, it will look "correct", and probably track and paddle well. If it is not symetrical, it will look wrong, and may have an exagerated tendency to turn.

I know where mistakes are in my boat. And there are a lot of them. But the boat paddles fine, and people are forever doing the "oh and ah" routine over it.