It starts when Madison is talking to Alex about how she doesn't know what to do about Scott (right before they go play on the water slides with Jordan and Griffon). Alex is wearing that white dress. Later in the movie she is at the party (when Jordan dedicates that song to her) she's wearing a different outfit, but then after the party (when she and Jordan kiss) she's wearing it again! Her hair is done the same way too! Obviously they did both of those scenes on the same day, but that's no excuse to keep her wearing the same outfit.