Yeah, the instructions are well hidden :-)
So, your boat. That kind of curve is not something you find with winding sticks. They're for twist, not curve. That curve is something you find by eye, sighting down the boat like in the pictures you posted. Usually that happens at stitching time. If the problem is caught then, usually some loosening and tightening of stitches will take care of it.
That's fine for your next boat, but you're looking for an answer for this one, where the problem's escaped. There's at least 3 choices.
1. SInce the curve is glued into the hull, you could unglue it and straighten it out. "Unglue" in this case means either soften the epoxy with a heatgun and pry apart the wood or use a razor saw to cut along the entire length of the glue line for the curved portion. Once the pieces are separated, they can be re-arranged so that the curve is fixed and then re-glued.
2. Sand away the portion that sticks out the wrong way and fill in the hollows with epoxy/woodflour mix. Restore the structural strength with extra fiberglass inside and out.
3. Ignore it. No one will see it unless you point it out to them and unless you're an expert paddler racing the boat the slight pull toward the curved side won't really affect your fun. It may require some corrective paddling strokes, but again, you'll be the only one who knows.
I would say that option 2 is the riskiest because of the amount of wood that would need to be removed. There's the risk of removing one side of the joint entirely. It would also have to be built back up very carefully to maintain the structural strength and symmetry. One approach is to just reduce the problem instead of trying to completely fix it, which would reduce the amount of sanding and rebuilding.
The saw work for option 1 is very fussy. Heatguns eliminate this but carry their own risks. Definitely practice with some test pieces made from scrap wood for either. If you are going with the heat gun, don't overheat. The epoxy will soften and be separable around 150 degrees fahrenheit (sorry metric world) and wood burns in the high 400's so there should be plenty of margin, but some heatguns are so powerful that even a moment's inattention causes trouble.
Hope that all gives you something to start with,
Laszlo