It's not about quantity. It's about quality.
Hurrying through mock exams without regard for what questions were right or wrong.... well..... that's just not using your time effectively. It's not the mock exams which will help you succeed. It's really understanding the concepts.... if you don't your mock scores won't get better, and you certainly won't pass for real. It would be like me answering questions about knitting. I don't know much about knitting.... answering mock exam questions will nit help me learn more. Studying, learning, and doing..... that's the answer.
I think going by exam domain (example, "Flow Control") and take those questions only, one by one and do an "open book" exam with the K&B
SCJP guide. Once you do that with each domain, you can take mixed mock exams. I'll bet you will score much higher.... and not because you remember the question/answer combonation. Also, on the questions that you don't understand,
you should be compiling and running the code, making changes and learning WHY something works.
Answering hundreds of mock exam questions from memory without adding knowledge will not get you as far as using the tools you have to REALLY LEARN the material.