Is the listing over yet? If not, you can retract you own bid. You should be aware, however, that there are only three valid reasons for a bid retraction.
1) seller changed the description after you placed a bid.
2) you accidentally entered the wrong bid amount.
3) you tried to contact the seller and couldn't do it.
Any other reason is considered invalid.
Here is eBay's invalid bid retraction policy.
Too many invalid bid retractions can result in sanctions from eBay.
The total number of bid retractions you have made in the last 12 months is shown on your feedback page.
If you ask a seller to cancel your bid,he can do so, but is not required to do so.he likely will though, then add you to his blocked bidder list.