Continuity mistake: In the opening scene the camera pulls back from a bedside locker to an over the shoulder shot of Kathleen Turner's character doing her make up in the mirror. Close inspection shows that the shoulder in the foreground is actually that of a double who doesn't quite match Turner's movements.
Continuity mistake: When Peggy Sue passes out at her reunion, the first shot (from her perspective) is her on the floor, looking up at her daughter and Charlie standing about 6 feet away. The second shot is her daughter and Charlie crouching down close to Peggy Sue's face. In the third shot, Charlie is instantly standing 6 feet away again.