This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
This really depends on the exam center that sold the certificate voucher to you. If the center allows it, you can postpone the exam. The best way to find out is to call them and get back to us with your results.