Step 18: The BeetleBot v2 ( Revisited ) - Making the shell ( part 2 )
I have file down the cap to make the entire cap rough. This will help the putty to grip. Let it dry and after you can file it again to make everything smooth. Once it's dry, I have used another putty for the finishing touch.
I did the same thing and filed everything.
If you don't have access to putty, you can use epoxy glue, it will work great. Let it dry 24 hours before sanding. Epoxy glue can be very liquid so be careful. Take your time.