Okay, so as far as I can remember (which isn't much) the movie starts of showing a girl who's in a closet (she's a child), she might've been crying, I forget, and then a boy (he's one too) comes to the closet door and tries to open the door to comfort her, but she pushes him away since he's fat and I'm guessing ugly, but as she's pushing him, she is transported to the future, when they're adults, where she works at a publishing company (I think, or something of the sort), and she meets him as an adult, and falls in love with him, but after how she treated him as kids, he doesn't love her, though he is friendly with her. She finds out that he is engaged to a woman, and on their wedding day, she realized she regrets what she did to him as children, and is taken back to when they were children and she was still in the closet and he hadn't come yet. When he did, she jumps at him and kisses him.
Woah, that was only a couple of sentences. Anyway, whoever knows this, please answer, and thank you for doing so!

13 Going on 30 (http://en.wikipedia.org/wiki/13_Going_on_30)