Factual error: Aphrodite mentions Medusa as her friend at point. She was a Gorgon, a monster, killed by Perseus, not a friend to any of the Greek gods.
Suggested correction: That's just the most popular version of the ancient myth. But because the story is based on a myth, and not real events, the story can change. This would be like pointing out a factual error for a film changing the origin story of a comic book character. In the poet Ovid's (47 BC - 17 AD) telling of the story, Medusa was a beautiful young woman who later was turned into an ugly woman with snakes for hair by Athena after Poseidon's actions.
Factual error: The bad guys are vanquished, and Wyatt boards the train and heads off into the sunset. Two problems with that scenario: from Los Angeles, heading West puts you into the Pacific, and Wyatt didn't have to take the train, he lived on West 17th Street, in Los Angeles.
Factual error: Right before Elvira is burned at the stake, the officer pronouncing judgement on her says "By the power vested in me, by the sovereign state of Massachusetts..." Massachusetts (according to its own constitution ratified in 1780) is a commonwealth, as are Virginia, Kentucky, and Pennsylvania. Although the internal governments appear to be different, they have the same legal status as states within the United States. (01:17:50)
Factual error: The closing credits give thanks to "FAO Schwartz", misspelling the name of the famous toy store with an extra "T".