Estes Space Ship One, Kit # 2191, Build Part 5, Squaring Up The Balsa

All of the laser cuts should be squared up.

In the end, the trailing outside fins will have to be perpendicular to the flat main wing.

Where my block wouldn't fit - 

The inside notches were squared up with a flat diamond file.

This flat edge is important so the long fin will glue on 90 degrees to the surface of the main wing.

The outside of the wing trailing edge curves out.

Wrap some sandpaper around a dowel to smooth the round inside arc.