While the airlines can be strict & have you by the balls once you get to the airport... there’s one tip you may have overlooked ???
The Department of Transportation requires airlines to “hold a reservation at the quoted fare for 24 hours without payment or allow a reservation to be cancelled within 24 hours without penalty,” as long as it’s at least seven days in advance of the flight date. That includes domestic and international carriers, if you’re flying to or from the U.S.