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

You're only chance is to run with her and gut it out to hold her pace. Your odds are not good and you are likely to get embarrassed by this girl (even at her pace). Pray for a cold snap and I hope you are in your 20s or 30s. With this heat, you are likely toast, but good luck.

My advice would be to own up before the race that you've embellished yourself and agree to start running with her going forward. That takes pressure off the race performance and you can walk parts of it without race day embarrassment from her.

If you have not run in years (or your life), you should be able to hold 9:30 pace for about a mile, but you will be gasping terribly. Even at 10/min mile (her pace), you will be struggling mightily.

I started running about a year and a half ago starting about 25 lbs overweight at 5' 10" and about 200lbs at 42 years old. I had not been a runner before. The first time I ran....let's say it was about a mile and a half and was not pretty.