Or on My eBay click on the little arrow, far right of the item on your selling page > End Item. On seller hub go to the Active listings page, select the checkbox next to the item you want to end and from the dropdown menu select End item.
If it is an item which has received bids, they all currently have more than 12 hours to run so you are in time to cancel the item, but you will pay a seller fee based on the highest bid placed for ending the auction early, as eBay see that the bidder will be disappointed , that the item has been withdrawn.
