Has the cloth got a selvedge i.e. woven or is it turned and woven. The results in the latter can be particularly skewed. See Fig 2 in my article http://www.scottishtartans.co.uk/Tra...e_patterns.pdf

Lots of steam and elbow grease is the answer for a woven selvedge but I don't know what the effect will be on a turned and glued hem .