The label provided by the seller through Ebay will be a standard small parcel label.
You will need to contact Ebay Customer services and ask for a new label.
Don't take your parcel to the Post Office with the unsuitable label on - you will just be sent off to get another label.
Use the link to contact Customer Services.
I would suggest you wait until tomorrow morning when you are more likely to get a call from Dublin.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
"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)