I totally get the stress of realizing you need more luggage space at the last minute! Last summer, I was heading to a wedding in Savannah and realized my "carry-on only" plan was a disaster once I tried to fit the gift and my suit inside. I panicked thinking I’d have to pay a fortune at the gate, but it’s actually super simple to do beforehand.
The best way to modify your booking is through the Delta Fly Ready app or their website. I just logged into my account, went to "My Trips," and selected my flight. There’s a clear option to "Add Bags." I did it about 20 hours before my flight, which saved me $5 compared to doing it at the airport kiosk. Plus, it made the bag drop-off way faster.