I always seem to get stranded in Charlotte - once with American and once with United. The first time with American, they had literally oversold the flight. I had my ticket in my hand, got to the gate, and the lady basically said "I'm sorry, there's not a seat left"
Uhhhh excuse me? I have a ticket? That I bought months ago? It's here, in my hand?
"There's nothing I can do, you'll have to go talk to the service counter"
There are like 50 irate passengers in line at the customer service counter. I waited, near tears, for them to tell me another flight didn't leave until the next night (it was night at the time), which meant all night plus a whole day in the Charlotte airport. No apology. No offer to set me up in a hotel. Nothing. Just "whelp, we can get you on the flight tomorrow night, even though this wasn't your fault in the slightest. See ya!"
I bought my tickets months in advance. I'd never had that happen before where they just didn't have a seat for a ticket they sold. So weird. Anyway...hopefully this won't happen and you'll be fine!!! Haha
EDIT: it was such a bad experience that I sent them a complaint via email and talked on the phone with the airline. They gave me a $100 flight voucher "for my trouble." I was like, uh thanks? I'm never flying with you again? Lol