The item will show as posted because you opened the label.
You can't update the tracking.
You have let the buyer know and, if the item did not arrive, you could add your tracking to any case opened.
That is as much as you can do.
"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)