At Georgia's party, Lindsey pulls the power cord out during the song 'Ultraviolet' and then goes on stage to talk to the crowd through the microphone, which shouldn't work due to her pulling the power.
In the scene where the Ace Gang "stalks" Robbie, Tom, and Dave the Laugh, you see that there are few people, a person standing, and an old couple right behind then when they do the dance that they made up. When it shows the boys again, and then goes back to the girls, you see that they have moved closer to the boys, but not nearly even that close.
In the scene where Jas first eats lunch without the Ace Gang and instead with Tom, Robbie has an apple on his lunch tray. From the distance, you can see him move his drink out of the way, but not his apple. When it zooms back in, the apple has switched from being on one side of his plate to the other side. Then, when you next see the apple, it has moved even farther towards the end of the tray, without giving Robbie time to move it while being un-noticed.
When Robbie's brother is wrestling with Georgia's cat in the park, his shirt is unbuttoned. When the four of them are talking together, his shirt is buttoned. Then when he asks Jas out on a date, his shirt is unbuttoned again.