I applied wood glue to the root edge and to the sides of the TTW (thru-the-wall) fin tabs.
The name letters should read clockwise, to the right.
Note how the letters lean down, like a down swept fin.
I drew an arrow to show how the fin should intersect the centerline of the body tube.

Here's all five fins viewed from the rear, spelling my first name.
I tried to fill the nose cone seams using medium CA glue and sanding to surface.
Well, the CA glue doesn't stick to this polystyrene plastic!
Filler/Primer and paint doesn't adhere to this plastic either.
Rough up the plastic surface before spray painting with color.
The upper picture shows a painting "handle" using a wrap of copy paper.