You most likely need to void it and make a new label.
If you've generated a tracking number and you have a picture of a shipping label on your screen, you cannot change any of the details anymore for that particular label (tracking number, weight, size, addresses).
Whether you have been charged for it is probably the only thing you really need to worry about.
Depending on what program/portal you are using to generate that label.
USPS especially once the label is created (i.e. you don't need to print it but it has generated a tracking number and you've been charged for it) you cannot change it or go to the post office and "add" postage to it.
Some programs will not "charge" you for the label until it is actually printed. I think Pirate Ship still does this with UPS labels.
