From the eBay home page, click the Sell option from the main menu. At the bottom of the next page is Selling Activities - click "See all" at the bottom of that section. That should take you to a selling info page and right there is a column of Manage Your Listing options. There's one there on ending your listing early. There's also the option of revising your item's listing/description. You can always let the bidders know about what you found and give them the option of cancelling their bid or not.
Good luck!