Hi...
There is now way you can "Accidently" buy an item on ebay because there is a 2 step process you have to go through...
First step...place bid or use Buy It Now
Second step...is to confirm your bid or Buy it Now.
Only the seller can let you off the hook, so contact them and see if you can resolve your issue, but keep in mind they are not obligated to do so.
One ebay there is a saying..
YOU BID
YOU WON
YOU PAY
If the seller dosn't let you off the hook and you don't pay for the item/s, you will have strikes placed on your record and many sellers block buyers that have strikes from bidding on their items and tooooo many strikes will get you booted off ebay.
So you better have your best Sunday typing finger on when you contact the sell with a email, be nice and beg for mercy.
Food for thought you could also pay for the item and resale it back on ebay and maybe recover some of the money or make some money.