Am I gonna get double charged?

I sold an item that weighed 1 pound and 8.10 ounces. Well I did what I was supposed to and I rounded up to 2 pounds. So it gave me the priority mail for shipping. I dropped it off at post office and I said "I think it's priority mail" She said "It weighed less than what it did so it'll be ground advantage".

I just hope Mercari won't charge me since the lady did ground advantage because I thought it had to be priority since that's what Mercari gave me I rounded the amount to 2?