Other mistake: In the final scene of the movie, Megan starts a boat motor and uses the propeller to hit Jason in the face, who has been chained down underwater. But if Jason can only barely reach her foot from underwater, there's no way the boat propeller is underwater far enough to reach his face. (01:17:50)
Other mistake: When Sissy gets up off the bed, if you look behind her you can see Jason going back towards the woods. He was supposed to be walking past their window which is why she saw his shadow.
Other mistake: When Nikki gets pulled in the bathroom in the RV, she's screaming and kicking all over the place making the door come way out. Cort couldn't hear her because of the loud music but he saw the struggle and did nothing.