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.
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 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.