When Michel was offering Ally and Melanie to go with him and Jean to see the real Paris. The words "We're so there." and "Let's go." were heard but Melanie and Ally are not saying these words as they leave the table.
Near the end, when the twins come into the dance, Jean gets the attention of Michel and points them out. Then the two take off their guitars. In the next shot where Ally and Melanie are talking to Jeremy, the boys are doing the exact same thing.
At the end of the movie, when the girls' grandfather says they can go to the dance, they rush out of the room saying they have to go get ready. Yet when they enter the dance, they are wearing the same outfits that they wore to his party.
When the girls are pressing their faces against the window in a locked car so Jeremy can't open it, you can clearly see an open window on the other side of the car, he could have unlocked the car himself.