If you are talking about the book you bought this morning from Thailand, you didn't bid you used a Buy it Now.
You cannot cancel it.
You have 3 choices.
#1 you get in touch with the seller and see if they will cancel the transaction. They are not obligated to do this.
#2, You can refuse to pay for it but this will get you a Black mark and will probably limit your buying on ebay.
#3, You can pay for it and then try to Resell it to someone else.