When Chloe, Riley, Dylan, Brian and Rachel are playing a game of catch to test each other on their knowledge of England, Chloe incorrectly gives the Queen's official title as "Her Royal Highness" (HRH) instead of "Her Majesty" (HM) - and neither her sister nor any of her friends correct her. In the British monarchy the style of HRH is associated with the rank of prince or princess, the Queen is HM which ranks above HRH.
When Riley (Ashley Olsen) is shopping, her hair is completely straight. Then when she is trying on the dress her hair is wavy. When she is walking with Brian, after trying on the dress, her hair is straight again.
In the beginning of the movie, when Dylan is introducing all of the members of the Model UN team, he says they are from "Fairview High". A few seconds later the team is introduced as being from "Lakeview High".