You can cancel a bid, but you will have to give a reason. Check the option that most closely matches your situtation, probably Bid Wrong Amount. I have been selling on ebay for over ten years and occasionally had a customer cancel a bid.
Sounds like a phony excuse for your foul up but immediately go to Customer Support and "retract or cancel bid". Ebay messages the seller who usually will cancel the bid. You will be notified by email.
You can find information pages on Ebay describing the rare cases where a bid may be canceled.
Here's a how-to by someone else.
http://www.wikihow.com/Cancel-a-Bid-on-e...
If no one outbids you and you win, then by ebay's policy you are obligated to pay. If you don't then the seller can open an unpaid item case. I would contact the seller asap and let them know what happened. Also look on ebay's help page to get more info.
If no one bids higher than you, and you buy the product, just call ebay or whatever you used to pay for the thing and explain to them it was a mistake. They'll cancel your transaction.
Once the bid goes through, you can request to cancel before you pay. There you can explain your reason.
immediately go to cancel the bid
Call their helpline number or Email them, tell your problem. or if you were looking something then use this bid.what's a big deal.
I would send the seller a quick email and try and explain the situation.