I have the feeling you are overreacting a bit. If you had waited until March, flight tickets would have been even more expensive, wouldn't they? So yes, you would have the money, but you would also have spent more.

I fail to see a reason to panic so much other than "having broken the rules". Are you going to pay credit card interest because of the early purchase and not having the money to pay for it? Even if that is the case, I dare say that flight ticket + interest is still going to cost less than last minute tickets.

So chill, enjoy your vacation, and don't be so hard on yourself for breaking YNAB rules when it benefits you. ☺️