If I had the power to go back in time once, I'd probably save that power like my rare potions in video games and eventually finish the game without using it.

For clarification, you can only go back in time, say, 20 minutes. I'd skip all the embarrassing things that have happened to me thinking there is something more important, only to realise when i'm 70 that I really fucked up when I was "X" years old and should have redid that moment.