Continuity mistake: When Bella and Edward are coming back from Port Angeles and see that their dads are still at the Police station, Edward starts to pull in and there's what might be an ambulance in the entrance. The next shot shows a semi-close-up of Bella asking Edward to pull in, which he does again, and this time there is no car in the entrance.
Continuity mistake: In the scene where Edward goes back to the highway from rescuing Bella. We see he stops the car when he turns, when the camera changes we see the area around them moving but we never heard or see the car accelerate.
Continuity mistake: As Edward and Bella are dancing on the gazebo at prom, the other two couples leave the gazebo. The first couple who leave walk over to the stairs and start walking down them. In the next shot they're still walking to the stairs and then begin to descend them again. (01:46:00)
Continuity mistake: When Bella says, "Why did you hate me so much when we met?" Edward's face is very close to hers and his right hand is placed with the palm on a branch. In the next shot, his face is further away, and now it's only his fingertips which are touching the branch. (00:52:30)
Continuity mistake: Just before the Cullens begin to play baseball you see Edward running away and beginning to turn around to look back at Rosalie while he is running. But in the next shot you see him walk with his back turned to "us" and then turning around to look at Rosalie. (01:16:10)