Did you place a bid or was it a "buy it now"? If you placed a bid, it was a binding contract. If it was a buy it now order, then, I think you should have the right to cancel it. Under the consumer law, you have a cooling off period. That's what I think. May be I am wrong. It is always worth to give it a try. Contact the seller and see if you can get out of it. A negative rating does not mean you can not buy from eBay again.
talk to the seller, he might still give you a bad review but it works.
tell him why you don't want the product anymore