That must have been quite a surprise for you and the turtle!
Around here I see a turtle about once a year, but last year one happened to pop its head up while I was blasting downwind on my raceboard. I missed him by about a foot.
Maybe we shouldn't talk about this though, or greenpeace will try to get raceboards banned for turtle safety reasons
Save the turtles, ride a twintip
Don't know if you can buy a single fin from Rista as a replacement? Maybe if you send it back, they can put it back in the milling machine and smooth out the area around the dent?