Just recently had a similar problem at the local fabric store, I had a lot of fabric on the sheet and she miscounted when she put it in the till, someone different had cut it, if was only 3.70 a meter and both the lady that had the mistake and the one that helped fix it was very gracious. Fixed it up in no time, (to save paperwork I just added the extra fabric to the pile) No feelings were hurt or anything, mistakes happen, everyone is human. Had they given me a hard time I would have been upset. I had about 15 fabrics and I only got a quarter meter of each.
I was there again today, this time, mostly one meter cuts, most were 3.70 a meter. But I had about 20 this time, the girls never complain when I do it, they usually make fun of it all.