Building The Card Stock Downscale Centuri Hornet Part 2

Before cutting out the fins, score the fold lines.
Carefully line up your straightedge before scoring.
I use the back end of a single edge razor blade. The metal rolled over blade top (Not the cut side, flip it over!) is a good scoring tool.

Tape over the sharp side with a few layers of masking tape so you have no chance of cutting your fingers!  

Here you can see the scored line on the black fin.
If you don't pre-score the fold line you'll never get a clean, rounded leading edge. 

Separate the fins from the cardstock sheet with scissors (See next picture)
Cut outside the edges, you'll cut to the final size after gluing and laminating.

Gently fold the fin in half down the scored fold line.
Don't make a hard fold yet.

Set some clean paper over the the leading edge.
Burnish and sharp foled with the back end of a Sharpie.

Right now you should have four fins, folded down the leading edge.
These are still a wedge shape, the trailing edge is open.