Get the item sent as soon as possible.
You could message the buyer to apologise for sending slightly late and to reassure them the item is on its way.
Sending items late can affect your account but you will still get paid.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)