There are several signs posted about the time of the prom, all of which say from 9 - 1. (One says 9 - 1 pm, which, of course, is incorrect.) Sue Snell asks the time at the family dinner on the night of the prom and is told that it is 8 o'clock. Shots immediately before and after the dinner scene show the prom going full swing, even though it is not scheduled to start for another hour. Additionally, it would still be light outside on May 25th at 8 pm.
Billy Nolan's car is seen briefly from behind, before Carrie rolls it, and the taillights are clearly those of a '67 Pontiac Firebird. However, when the car is overturned, it becomes a '67 Chevrolet Chevelle.
When Carrie is pleading for help in the opening shower sequence, she grabs Sue Snell's arm twice. Both times, Sue dodges and pushes Carrie away. In both pushes, Carrie grabs the same spot and Sue ends in the same position, revealing that the two pushes are the same push shot from different camera angles.
In the gym scene where the girls are told about getting detention or refusal of their prom tickets, Chris' lip gloss disappears and reappears. When she takes the gum out of her mouth she has lip gloss on. It then disappears and reappears as the scene goes on.
When Miss Collins is pacing in the principal's office after the shower incident, she pauses in front of his desk. Carrie's blood is visible on her shorts, making the principal uncomfortable. She then continues pacing around the office and the blood disappears. Although she is moving, her sweatshirt would not move that much as to cover all traces of the blood.
When Miss Collins begins calling the roll, the first shot reveals a girl dressed in dark blue sitting among several girls higher on the bleachers. In the next shot, she's sitting in the front row next to Helen. But in the shot after that, she's in her original place.
When Carrie goes to kill her mother, she impales Margaret's wrists with knives through her palms. When she dies moments later, her body remains completely upright.
Her body would sag, and the knives could not hold up the weight of her body.