When Aubrey and Dave are driving after he picked her up at her house, Aubrey's hair is curly. When she steps out of the car on the parking lot, her hair is straight, and in the next scene, the kissing scene in front of her house, her hair is curly again.
During Dave and Aubrey's first meeting when they are talking in the back alley at some point Dave sits down and you can see just the tip of his left foot in the narrow path.In the next scene when a guy with a skateboard comes out and uses this path you can see that both of his feet are in the path and he is forced to pull himself back.
Dave receives a text message to his iPhone from Aubrey. His phone is on the passenger seat lit up showing the time as 1:57. Seconds later he picks up the phone to read the text and it shows the time as 11:15.
After Dave jumps from the roof he says he is OK but in the next scenes and in the movie theater you can see he had actually scratched his hand and is wearing a small bandage.
During their talk in front of Aubrey's house when she is leaving to take the bus for school, her hair (bangs) change many times. You can see it is split in half in distant shots, and straight on close-ups.
In the final scene where Aubrey decides to run back to Dave, who is still at his car, you see her drop her bag to the ground to make out with him. In the next scene however, they change the camera angle of them making out, and the book-bag is nowhere to be seen.
In Aubrey's room, you can see two windows. One in the side wall, and one in the corner of the wall behind her bed.
When Dave is leaving through the window (presumably the bathroom window), you can see that the house does not match her room configuration, as there is no window in the bed wall corner from outside.
In the final scene, when the bell rings for the first period to start, there is no reaction from the extras in the background, who continue acting the same way as if nothing happened.