re: I lied to a girl I'm trying to impress, told her I can run a 5k in under 29 minutes (DONE)

As others have said, I think trying to stay with her is your best bet. It’ll give you the motivation to keep going when you mentally feel like you can’t anymore (probably around the 3/4 mile mark). If you told her 29 minutes, she’s obviously not expecting you to be some incredible runner, so you struggling throughout shouldn’t be a problem.