Throughout most of the movie, Sutter's car is a 1995-97 Honda Accord, but when he and Aimee sit on the back of the car, it is a 1993-94 Accord - note the smaller taillights.
When Sutter and Holly are talking on her porch, Holly is looking up in some shots as though Sutter is higher than her (standing?) whereas in others he is looking straight at Holly and not down like he would be if he was standing (or higher). Both their heads are level with the same part of the chairs they are sitting on.
During the love scene between Sutter and Cassidy, they can be seeing on bed close to the window and the room is dark due to drawn curtains. But when the shot cuts to Cassidy's face, it can be noticed that she is positioned slightly far away from the window and the room is now substantially brighter.
When Sutter and Aimee are at the prom, they are drinking out of two cups. One cup is blue and one is yellow. When Sutter returns to the table after a dance with another girl, his cup is a different color than it was when he left.
After prom, Sutter's tie is dangling around his neck. It is a pre-tied bowtie not a regular one but he works at a tie shop.
The maths question to Sutter after he is held back after class: "one acute angle is twice the other, what is their sum?" is an impossible one. The question should have begun with "In a right angled triangle...". The answer is 90º.
When Bethany and Tara drive up next to Sutter and Ricky, a view from behind both cars reveals that they both have the same license plate number.