Maybe that leaf got a little too much heat at the wrong time, maybe not, who knows. It looks like the subsequent leaves are properly formed and won't curl. I don't see a big problem here, just a temporary hitch. If the leaves continue being smallish and curled, then I'd start worrying.

Thanks for the reply.
My original posting is almost a month old and since then the plant somehow pulled itself together and seems to be growing normally. No more curling, whiteness or bug bites.

why the netting?

The netting is to keep the pickle worm egg laying moth away.

ah, glad to hear that the natural order of things prevail and your kabocha is thriving.