I’d guess it depends why you were last to board. I was supposed to DH in SWA last month and they wouldn’t book my ticket until the day of (which means I couldn’t check in until a few hours prior to departure). They ended up booking me on Delta instead but I was ready for a fight for the 1.5x since it was their fault I’d be in the C group. Anyway, if you had an A or B boarding group assignment and just didn’t get on in your group I think that’s on you. If it’s the company’s fault then I’d pursue it. Good luck as I’m sure no matter what the company will try to deny it.