While Dot is strangling Paul, some blood drops fall on the front of Nina's neck. In next shots of the strangling, the blood drops switches from the front of Nina's neck to the side then it switches back again to the front.
When Dot and Nina arrive at the dance and Nina leaves to smoke you can see the backpack on Dot's back. When Conner comes up to Dot to talk to her the back pack is gone. In the next shot, it is back.
In Nina's bedroom, the picture on the wall of her and Michelle is straight, then crooked, then straight again.
At the dance the guy puts Dot's bag flat on the chair but when she looks at it moments later, it's standing up on the chair.
At the beginning of the film when Nina and Michelle are eating sweets in the canteen and they're talking about Dot, Michelle's sweet is red but in the next shot when she goes to eat it the sweet has changed to green
When Connor is describing Hershey PA to Dot, he tells her that they give out free M&Ms. They are a product of the M&M/Mars company, not Hershey. Hershey does in fact give out free candy but it is always a product of theirs, not the competition.