Countmyblessings if it was a routine scan (12 weeks?) where they saw your MMC theres usually no mistaking it due to what you would be expecting to see at that gestation or even a couple of weeks either side to allow for incorrect dates.
This article is dealing with very early scans I think where the margin for error/change in dates etc is much bigger so waiting is advised rather than straight for abortive action.
Hope that helps a little, I cant imagine how horrible it must be to get the worst news when you arent expecting it x