Once you agreed to the terms and conditions, confirmed and submitted the bid, it cannot be retracted. Because bids are permanent, when you bid you are given a second confirmation that must be agreed to before placing the bid, so you have that opportunity to click cancel. Please review that message before clicking 'confirm' as it will verify the amount being bid, and the item the bid is being placed on.
Once a bid is placed we can not allow bids to be retracted as it undermines the fairness of the process for all participants. We can not contact other bidders for that lot, nor can we remove the bid.
If you have made this error 24 hours before closing, there is a good chance you are going to be outbid as bidding gets competitive in the last day of closing. However, we can not guarantee that, and if you do win you will be responsible for that lot- which includes paying for and picking up the lot.
Please note that you can adjust your own maximum bid to the current bid level. Please see this FAQ for more info on how to adjust your maximum bid.