This is between you and the buyers, if they want to leave a negative they can. You admitted fault and if buyer wanted to ask a mod to revise that would be up to them but a mod will not remove any feedback like this for a seller. You will need to work it out with the buyer and have them ask for the negative to be removed.
Collecting: Football-RG3,Alfred Morris Basketball-Kyrie Irving, Bradley Beal Hockey-Ovechkin, Backstrom Baseball-Bryce Harper
"If it says OBO then send me an offer, do not ask me to give you one"