I used Hugin to stitch a bunch of building site blueprints just last week. It was painful... just very unintuitive and hard to grasp. Very powerful software though. Just keep in mind it was built to stitch panorama photos, compensate for lens deformation, point of view, etc.

Stitching flatbed scans is not the best use case for Hugin and it shows.

I used the same tutorial linked by Op http://hugin.sourceforge.net/tutorials/scans/en.shtml

Note that Hugin requires overlap between scans. I would test MS ICE first if I were you (less powerful, but way simpler) https://www.microsoft.com/en-us/research/product/computation...