Continuity mistake: At the beginning of the movie Margaret White gives birth to Carrie. She gets a pair of scissors out of a drawer and tries to stab Carrie in the face. When Carrie starts to cry Margaret picks her up and holds her near her face and the umbilical cord has disappeared. It was there before she picked Carrie up, and she never cut it.
Revealing mistake: During the prom sequence, when the moon-shaped light fixture falls onto the stage supposedly "setting the stage on fire", you can see that it is a fuel line that is starting/controlling the fire.
Other mistake: The alternate director's cut ending available for viewing within the movie via seamless branching on the Blu Ray is very lazily cut into the film. The music from the previous scene cuts out abruptly when the scene begins, Sue's stunt double's face appears in a close-up shot, and the music from the ending credits abruptly cuts in partway through the song (rather than starting the song from the beginning) once the alternate ending is finished playing. The very end of Carrie's scream from the theatrical ending can also very briefly be heard at the same time the music begins.