On the tail cone there is a recessed ring. This leaves a gap at the root edge of the fin. You were told to make a triangle shaped piece of balsa, insert the piece and glue. Trim off the excess and apply a glue fillet along the root edge.
I mentioned this to Estes. Maybe it'll be incorporated in a future run of kits.
The scale fin tapers can be done with patience and a good sanding block.
This shows the fins and gap at the tail cone.
Sanding the suggested scale diamond taper looks okay but with the 3/32" thick fins the effect is subtle. If the fins were thicker the taper lines would be sharper.