Continuity mistake: When Ellen is getting up from the table after arguing with Jill, she takes her purse off the table with her right hand. In the next shot, she's shown dragging her purse across the table with her left hand.
Continuity mistake: When the boy is hit by the basketball thrown by the sports instructor, he's hit in the right shoulder, but grabs his left shoulder and says "ow".
Continuity mistake: When Ellen walks in on Vlad and Di, she drops a small backpack or a purse next to the wall and walks out. The shot goes back to Vlad and Di, then back to the empty doorway but you can see the floor and no purse or backpack in sight.
Continuity mistake: When Ellen is found by Vlad on the roof, the scene starts with a closeup on her CD case which is right in front of the CD player, but in the wide shot, the case is nowhere to be found.
Other mistake: When Ellen's brother leaves the bathroom as she's taking a shower, she opens the shower curtain to check that he has left. At the point she opens the curtain, you can see the top of the bathing suit she was wearing in the shower.