I read a book when I was about 11 that was about a girl who had an alarm clock that she set and when she woke up in the morning, she was the age of the time she'd set (hope this is making sense...!).
She went back to her childhood and also forwards to her future and met her children-to-be. Then she came back to the present and had to decide whether she wanted the future she'd seen.
Does anyone know the title? I've looked for it occasionally for ages, but not found it!