Song from A Cinderella Story!?

During a scene in A Cinderella Story( the dance scene where Hilary Duff walks down the stairs in her dress) there is a song playing called best day of my life. Unfortunately, when they released a soundtrack for the movie the song was on it however it was re-done by Jesse McCartney. This is not the original version of the song that played in the movie and I'm wondering if anyone knows where I could find the original version. Please and thank you!