It is literally impossible to "accidentally" place a bid. You must manually input your username and check a box next to "Yes, I wish to bid!" to confirm that you would like to bid, then click the button that says "Place bid!" to actually bid.
You will need to speak with Xanthochroid and explain the situation to him/apologize and see how he would like to proceed.
We do ban players from the auction house for placing bids they do not have funds for or do not intend to follow through with.
