Factual errors: The film claims that that Eric Harris and Dylan Klebold attended a bowling class earlier on the morning of the offense. This is incorrect as testified in a judicial review.
Revealing mistakes: As Charlton Heston walks away from Michael Moore in the final interview, the scene cuts repeatedly between Heston (point of view from behind Moore) and Moore (point of view from the stairs directly in front of Moore) holding a photo of the slain Flint, Michigan girl and asking Heston to look at it. When the POV is of Moore holding the photo, there is clearly no cameraman anywhere behind him. The same with the POV of Heston, there is clearly no cameraman anywhere in front of Moore. So the two POVs were not filmed simultaneously as the film implies.