Continuity mistake: When they are on the back porch, watch the Coke bottle. The level of the liquid in the bottle goes down, then up, then down, etc.
Continuity mistake: In the very last scene Marilyn Monroe throws Tom Ewell the shoes he forgot to put on. He thanks her and waves, with one shoe still held in his hand. He turns round and walks away, with both shoes on.
Continuity mistake: Watch the label of the coke bottle in the porch: It moves around depending on the shot.
Continuity mistake: The first time Tom Ewell trips with the rollerskate his trousers get wet. In the next shot they are dry.
Continuity mistake: Tom Ewell turns the record player off twice toward the beginning of the movie. He turns it off before the janitor comes in, then he turns it off again after the janitor leaves.