most campgrounds I have been in stick my reservation/receipt/etc. in a slot for that specific spot I am in. wouldn't think they would pull it and throw it away if it clearly shows two nights paid. I would be irate for the inconvenience but since they had a better spot no harm, no foul
I had a similar/worse thing a lot of years back when I rented the bottom floor of a house. told the owner I was leaving at the end of the month, started moving out earlier, went back one day before end of the month and my key wouldn't work. found out how easy it was to kick in a basement door. got the rest of my stuff.
bumpy