Enerjet by Aerotech, Astrobee D Build, Part 3, Fin Prep

I'd recommend taping off the outside half of the fins. It's easy to scratch the fin face with the sanding block when sanding down the nub. 

Notice I'm using my thumb as a "bumper" so I can focus the sanding just the nub.

Earlier I mentioned one side of all four fins has a recessed nub. Just sand down the raised side of the nub.

On the left you can see the area that needs to be filled.

If you don't have Tamiya putty, 

You can use a bead of medium Super Glue. The medium glue "beads" and won't run as easily. I pick up this CA glue at the Dollar Tree store.

 

On the left is the CA glue bead. Be patient, it will take a while to dry.

Sand with 220 grit on a block and follow with 400 grit.

On the right is the finished fill. Run a fingernail over the hard clear fill to see if there are any dips. You may have to do a second application.