I am not your lawyer but here's the deal about your situation.
eBay in general requires that all auction except for real estate and car auctions are binding legal contracts.
Auto and real estate auctions are in no way binding at all on eBay and the only consequence to backing out is having your account possibly warned or banned.
The only exception to this is if your state has a law about "auctions" which makes them legally binding. The good news is that your state does have such a law:
§ 2.328. SALE BY AUCTION. (a) In a sale by auction if
goods are put up in lots each lot is the subject of a separate sale.
(b) A sale by auction is complete when the auctioneer so
announces by the fall of the hammer or in other customary manner.
Where a bid is made while the hammer is falling in acceptance of a
prior bid the auctioneer may in his discretion reopen the bidding or
declare the goods sold under the bid on which the hammer was
(c) Such a sale is with reserve unless the goods are in
explicit terms put up without reserve. In an auction with reserve
the auctioneer may withdraw the goods at any time until he announces
completion of the sale. In an auction without reserve, after the
auctioneer calls for bids on an article or lot, that article or lot
cannot be withdrawn unless no bid is made within a reasonable time.
In either case a bidder may retract his bid until the auctioneer's
announcement of completion of the sale, but a bidder's retraction
does not revive any previous bid.
(d) If the auctioneer knowingly receives a bid on the
seller's behalf or the seller makes or procures such a bid, and
notice has not been given that liberty for such bidding is reserved,
the buyer may at his option avoid the sale or take the goods at the
price of the last good faith bid prior to the completion of the
sale. This subsection shall not apply to any bid at a forced sale.
In other words unless the car is in a forced sale ie the sherif or bank is auctioning it then if the seller received a bid on a non-reserve auction you may take the goods at the winning bid price.
Legally the car has been sold to you and you own it if you make out a payment in the full amount for the auction. The law is very clear in your situation. You have the right to take the car.
Hope that helps.