Other mistake: In the first scene with Randy telling Jamie Lee Curtis to turn around, the reflection in the TV never mirrors the actual position of Jamie Kennedy. (01:22:30)
Other mistake: Tumbling down the ditch with Dewey, you can see that Gale loses her red pumps. In the rest of the scene though she goes to Mr. Prescott's car first and then back towards the street without fetching her shoes back. (01:17:55)
Other mistake: During Tatum's murder we see some problems exacerbate. The killers are not supposed to be invulnerable and are wearing a cheap costume, but they receive hard hits (Tatum breaks two bottles of beer, one straight to the face) and they don't have a single scratch. When she is killed, nobody hears her scream and nobody else needed to grab a beer either. Furthermore, Ghostface has the garage door fully open, but without knowing who is on the other side, that is one room away from the others, goes by the mysteriously unlocked door to the inside of the house. And we see Billy (who should be the killer there, since Stu was at the party) join in coming from outside.
Other mistake: Randy answers the phone and receives the news that the principal has been killed and left to hang from the goalpost. He gets the call from the telephone by the TV, and he his head reaches about half the height of the TV. The hidden camera is on top of the VHS player, a shelf underneath the TV, but somewhat Gale and Kenny in the TV truck get a close-up of his mouth. (01:16:00)
Other mistake: When Stu brings Sidney's dad out in the kitchen, you can see behind him a September 1996 calendar. Earlier in the movie, the scenes inside Principal Arthur Himbry's office do show a September calendar, which is obviously the intent of the movie, but it's a September 1997 calendar.
Other mistake: Two police officers drag Billy Loomis out from the sheriff office across the station; the younger officer stares into the camera right before it cuts away. (00:34:40)
Answer: Landline phones like the one used in the movie cannot dial out a phone number while the line is active. Considering the killer is continuously calling her, she can't dial out on the phone line. This is referenced in the movie itself when her parents arrive home, attempt to dial 911, and can't due to the line still being active.