Continuity mistake: When Ryan is lighting Marissa's cigarette with his, at the start of the shot it's full, then the shot goes to Ryan and it's still full. But then the shot goes to Marissa and if you look at Ryan's cigarette you can see it is almost all gone. Then the shot goes to Ryan and the cigarette is full again.
Continuity mistake: When Marissa is dumped on the driveway by Summer and Holly, Ryan first sees her there her left arm is across her chest with her elbow sticking up. The next shot of Marissa her ams are straight and spread out, and the next they are close by her sides, which is impossible for her to have moved them herself as she is unconscious.
Continuity mistake: When Kirsten and Ryan are talking while setting up for the Casino Night, the camera cuts between Ryan And Kirsten while they talk. Whenever you see both characters in one shot, her fringe is forward, but when you see the individual shot of her, her fringe is pulled back behind her ear.
Continuity mistake: At the part where Kirsten brings Ryan and Seth to help set up the hall, Seth starts to blow up balloons with helium. In one shot he has an orange balloon under his arm and is tying the bottom, and the next he's starting to fill up a different balloon, without time to finish tying it and pick up a new one.