If you are having second thoughts then file for a bid retract otherwise do not worry about getting screwed over or anything like that. Personally I would not buy a complete bike from ebay simply because I perfer to give buisness to local shops in my area along with getting full service, warranties etc.. However if the price is right then who knows, I could be swayed.

So if you win the bid, then yes your stuck with the bike though you could always try talking to the seller. Otherwise you will get a negative on your feedback if you bail on the purchase.