The length of Nicole's hair is different when she is on the school news from when she is at school watching the news. The news was supposedly filmed the same day (as you can see, since she is wearing the same shirt), but her hair is clearly a different length.
At the beginning of the Centennial Dance, Nicole has more than one earring in each ear. A few seconds later when she is talking to Alicia she only has a stud in each ear.
When Brad and Alicia are talking in the restaurant, Brad's bangs/hair keeps moving from gelled back and hanging down in front of his face.
When Nicole and Chase go "cruising Broad Street", the roof of the car is clearly down. In the close-ups during their conversation, the roof of the car can be seen above them.
At the dance, the Electrocutes are playing on the stage and there is a banner with their name on it in the background. Near the end of the dance scene, the Electrocutes are still singing, but they (and their sign) have disappeared from the stage.
When Nicole and Chase come home from the Centennial Dance, the sky is slightly lit, because they were out all night and the sun is coming up, not because they left the dance very early.
In the lunch scene when Chase and his friends are pulling the prank on the rest of the class, the video camera which is supposed to be taping the prank is turned off.
Even though the movie is set in the fall (Nicole's father asks her to come ballooning with him in three weeks at the beginning of November), it's basketball season at Timothy Zonen High. High school basketball is usually played in the winter.