When it dries, wet sand

And, the more 'drying time' you can give it, the better your results IMO.
Especially if you have laid in quite a few coats to fill the scratch, leaving for a month (depending on the temperature in your kayak storage area) would not be too long before trying to level and rub out to a glossy finish.

Soft spar-type varnishes don't polish out as well as harder finishes, so you need to give it the best chance possible to harden.
IME, of course.