I coated the print side of the fin pattern with medium CA applied with a Q-tip. Go lightly, you don't want to smear the ink. The CA coat will gray up the white card stock slightly.
Pre-score the fold lines. It's easier to do now before the fin can is cut off the instructions.
I used a straightedge and the back side of a razor blade. Tape over the sharp side with a few layers of masking tape. You can also use the tip of a dull butter knife, not a serated knife.
Cut the outside and center squares then cut and remove the fin can piece.
The inset shows how the fin can folds in.
Art Applewhite must have done a bit of Origami in the past.