Continuity mistake: When Sam and Danny are talking and Danny jokes about having a kink for women who are ashamed to be seen with him, he goes from having his head tilted to the left to suddenly being tilted to the right between cuts.
Continuity mistake: When the girl throws soda at Sam's chest and calls her a "murderer," watch closely. As Tara and Chad hold Sam back, they swap which side of Sam they're on multiple times depending on the camera angle. The way Anika is holding back Mindy also changes between angles at the same time.
Continuity mistake: When Sam and Tara are arguing after they leave the party, watch closely. The back of Tara's bandana moves on and off her shoulder repeatedly as it cuts back and forth.
Continuity mistake: When Chad is trying to psyche Ethan up to go talk to the girl at the party, when Chad says "You got the confidence!", pay attention. Chad's hands go from down by Ethan's waist to up right next to his shoulders between cuts.
Continuity mistake: When Chad and Ethan take the shots at the party, in between shots, the shot glass goes from being below the camera to being upright at his mouth between cuts.
Continuity mistake: When Mindy and Anika are at the party, and Anika says, "Being at a house party after you were almost brutally murdered at a house party," pay attention. Anika pretty blatantly goes from facing away from Mindy to facing Mindy between cuts.
Continuity mistake: When Sam is at her apartment at the beginning of the film and is talking to Quinn before going to find Tara at the party, pay attention to Sam's hair. There are multiple times with the amount of hair that is in front of or behind her shoulders changes as it cuts back and forth between her and Quinn throughout the scene.
Continuity mistake: When Sam returns to her apartment at the beginning of the film, she is carrying two envelopes. When she hears the noise and turns around scared, she goes from holding the envelopes in just her left hand, down by her waist, to suddenly holding them with both hands up by her chest between cuts.
Continuity mistake: When Jason collapses after being stabbed, the pictures on the refrigerator behind him change slightly between edits, as it cuts to a wideshot. It happens quickly, so you have to pay close attention. (Like some of them shifted during the different takes as he slid down.)
Continuity mistake: After Jason washes his hands, his phone rings. In the wide shot, his phone is about 3" from the edge of the counter. In the closeup, the phone is actually hanging about 1" over the counter.
Continuity mistake: When Jason is looking at Professor Crane's dead body, the amount and pattern of the blood on the front of her dress, and the position of her head changes slightly between the two shots we see her. There is significantly more blood in the second shot, and her head is tilted down a bit more.
Continuity mistake: When Professor Crane is killed, the amount and pattern of the blood dripping from her mouth and down her chin changes subtly between shots, at one point.
Continuity mistake: When Professor Crane is in the alley and the Ghostface voice says "No, it's not," she's scared by four people in Halloween costumes behind her. The way they're standing and walking by changes between shots.
Continuity mistake: When professor Crane is texting her date, at one point she reaches over and takes a quick drink in a wide shot. The editing is awkward. In the closeup, both of her hands are on her phone. Then, in the next shot, suddenly her left hand is reaching towards her drink. Then she starts to move her hand back towards her phone, but it cuts again, and she's instantly holding the phone in the EXACT same way as before. It looks like the shot of her taking a drink was cut in to break up the phone shot.
Continuity mistake: When Professor Crane picks up her phone for the first time at the beginning of the film, the way she's holding it in her hands changes slightly between cuts.
Continuity mistake: At the beginning of the film, when Professor Crane's phone first buzzes, her right hand goes from near the right side of her face to down over her left shoulder instantly between cuts.
Answer: I think this is more "trivia" than mistake. There's no error in a film taking place a bit further ahead in time than in its release date.
TonyPH