You can ask the seller to remove your bid, or you can do it yourself. To do it yourself, have a look at the following link about retracting, - there is a Bid Retraction form near the bottom you can use:
http://pages.ebay.ca/help/buy/questions/retract-bid.html
And just so you know, retractions are generally not the done thing, hence they are displayed on your feedback page. The retraction and the reason for it appear on the bid history page of the item, and you are expected to enter the correct amount after you've removed the first mistake. On the bright side, yours is one of the few valid reasons for retracting. In future, be very careful with that bid button, and double check the amount before confirming.
Good luck. 🙂
