Hi Thor

There are brilliant kayak builders .... then there is me, who relies on smoke and mirrors.

I found the best way to sort out gaps was to glue slivers of scrap strips pushed into the many gaps in my build.

Hopefully picture attached of a ratty strip woopsie.

If I matched my strips better ... even I wouldn't notice them. Remember that at the end of the day, the finished kayak is viewed from a distance and holistically by most mortals ... and any (perceived by you) blemishes will not be obvious.

Filling can work, but you probably need to epoxy the project, then fill gaps with dookie schmooze (wood chalk - really, really fine dust mixed with epoxy) then sand. Because the dookie schmooze is hard, sanding is not easy. Why the pre expoxy - that will stop epoxy stains blotching up your work, and helps prevent sanding hollows in the vicinity (the epoxied filler is hard, while the surrounding wood is soft which has to end in a donut hollow?

It is difficult to mix up consistent coloured epoxy dookie schmooze (because you can never do it all in one go)

In contrast your glued slivers of wood sand down easily and will probably match pretty well.

Just my preferred fix - there is more than one way to skin a cat.

Happy building

Pete