There are very few reasons allowed for Retracting a bid, although personally I think "I didn't read the description" and "I changed my mind" should be allowed.
Since these are not acceptable reasons for Retraction, you can Contact theseller, the link is on the description, and ask him to cancel your bid. He is not required to do this but most will. Of course you will probably also end up on his Blocked Bidder List.