Instead of watching a movie of his birth, he watches a movie from an early birthday party in which Kayleigh was present. He then told Kayleigh he hated her, so she went to live with her mother, had a good life, as does Evan and Lenny and Tommy. In the present, Evan and Lenny burn the journals and Evan is apparently some sort of besuited muckety-muck when he sees a grown Kayleigh pass him on a crowded street. He stops and does a double-take, and then the movie ends.

He also burns all of his photo albums and movies after he "fixes" things foor the last time

In the director's cut, he watches a movie of his mother giving birth to him. He assumes the body of himself as a infant, still in the womb. He proceeds to choke himself to death with the umbilical cord and she has another stillborn baby, as mentioned earlier in the film(she said that she had 3 stillborns before he was born). He was never born, and everyone's life was much better. It goes through the same sequence of Kayleigh moving away, getting married, etc...It was a much better ending to the film.

baby choking himself in the womb

Donnie Darko