Once you have every impotant point of reference recorded, anchor the storyboard to your new sheet of wood and transfer all the points back off the storyboard.
Connect the dots, cut all the cuts at the proper angles, and it should fit. And it usually does, amazingly well.
This evening I did the majority of the cleaning and smoothing out of the gutters, using a variety of strange, loud tools. There’s still a bit of hand work to be done before we glass the decks, but its pretty close.