Continuity mistake: At the battle of the bands Ryan's car is smashed by Tyler and his friends, specifically the windscreen and headlights. When Elissa drives the car minute later, it is in perfect condition. It's also in perfect condition when Ryan later reverses it into the garage.
Continuity mistake: During one of Elissa's phone calls with her mother the phone switches hands between shots without enough time for Elissa to have put the phone in her other hand. In one shot its in her left hand and in the next its in her right. I cant remember how far into the movie it is.
Answer: SPOILER ALERT: There actually were two siblings at one point, Ryan and Carrie Anne. The young Carrie Anne dies in a swing accident. In the end, we learn in flashback that the parents, who blamed Ryan for Carrie Anne's death, proceed to punish him by making him dress up as Carrie Anne and take her place. When he protests, he is physically abused by his mother. So, it isn't Carrie Anne who wanted to be a boy called Ryan. It is Ryan who was forced to take the role of his dead sister, Carrie Anne. Eventually, in the persona of Carrie Anne, Ryan kills his parents, and proceeds to find women whom he tries to transform into his dead sister.
Michael Albert