Unlike other certifications, OOAD needs to apply your knowledge on case studies. Also it is not like reading something and puting it there directly. It is not straight forward. Since you have felt what the exam is like, I am sure you will make it next time. Along with 2 prescribed books, try WhizLab software. Whizlab software will give good number of practice questions , that will help you to align your thinking in the way exam expects.