If I had to redo this project, I would choose a different method than what I'm about to describe:
Taking my fitted fins, I carefully, one-at-a-time, glued each fin onto the rocket body, using CA glue. Aligning and straightening the fins proved difficult and unwieldy, and I was never quite sure when the glue would decide to cure. Also, until I got three of the fins attached, it had difficulty balancing. After I attached the fins, I coated them with a thin layer of super glue to get them to match the aesthetic of the redheart cap.
Instead, I would recommend cutting a slot in the bottom of the rocket body, and placing tabbed fin cutouts into the slots at the bottom of the rocket. It makes alignment, shaping, and glue-up way easier. If you do this method, I would recommend finishing the fins before you attach them, using a quick polyurethane coat to avoid cloudiness that can be associated with super glue finishes that aren't applied in a thin coat.