Factual error: The problem with firing a cannon on steam power is to have the boiling water build enough pressure inside the barrel, with no leaks or openings to release it before its time. The professor's scarf and the plug hammered into the fuse hole (which also flies off just before the shot) wouldn't be good enough as pressure restrainers.
Revealing mistake: It is obvious that the night scenes were filmed in broad daylight, since clear shadows are still cast on any available surface.
Other mistake: When Krolock ambushes Sarah in her bathtub, he bites her well above the place where the bite marks later show.
Factual error: I don't know whether they had bubble baths in an isolated village of the late 18th/early 19th century; and even if they did, the foam in Sarah's tub looks remarkably untouched (except for the blood) - considering that she had just been thrashing around in it when Krolock attacked her.