This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
One thing suggested in the Sierra and Bates book is to note your weak areas. Go through the mocks (or end of chapter exercises) and write down why you got each one wrong. Maybe it was a fact (knowledge). Maybe it was missing a detail like missing a catch block.
Then look for trends. Do you need to memorize key facts? Do you need to slow down? Do you need to have a mental checklist for finding certain issues? Do you need to write more hands on code.
December 19th is still over 2 weeks away. Don't worry. You can get your score up in that time. Just don't keep doing the same thing. The introspection described above will get you over that hurdle and using your time productively again.