Hi
I believe its good to have a thorough go through of Two-minutes drill in K&B book. You could try the Sun's free proficiency assessment
test which is really good where you can learn very important minute concepts which you might have missed or not noted.
The link for Sun's e-practise exam is :
http://www.sun.com/training/certification/assessment/055-Jintro.jsp You can try some of the mock tests that you can find the link in the
SCJP FAQ in Javaranch. After the mock-tests have been taken its vital to note down the points where you went wrong. In this way, you will not repeat the mistakes in the real-exam.
I surely would say to keep cool but that does not mean to freak out. However, it varies from person to person. You could reread all the concepts you have learned so far, that will surely help.
Hope this helps.
Greetings
Kris