I've described how to shape this style fin in the past on the blog:
And in the Apogee Peak of Flight newsletter:
Just what you wanted - HOMEWORK!
I won't be going into detail on how to shape the fins here on the blog. Use the addresses above to see one way to do it.
Shaping Nike style diamond tapered fin requires harder wood. The final fin shape will be thin.
There is so much extra wood on some laser cut sheets I cut more fins from what was left from the harder kit sheet.
With the edges glued back to back I had enough area in the center to cut four more fins.
Sand the edges flat and glue them back to back. The pencil tracing shows how the new fins were drawn.