A couple of printer settings make the folds line up perfectly.
100%
Print at 100% / actual size.
Turn off “Scale to fit” or “Fit to page” — the sheet must print true size.
2×
Print on both sides.
Choose double-sided / duplex, and flip on the long edge.
Better on a big screen
The design studio uses drag-and-drop in 3D, which is much easier with a mouse and a bigger screen. You can keep going here, or open Draw ’N Fly on a computer for the full experience.