Don't try and take the PMP exam immediately after your PMP exam prep class. Similarly, don't wait for months either. The right moment is usually between 2-5 weeks after you finish your class. A good PMP Exam preparation course provider will tell you to do more reading and practice exam questions. They should also direct you to training products specifically designed for the purpose. Additional, on-line or software based training products with training materials that provide you with your 35 contact hours of project management training plus the exam preparation materials that get you ready to pass the exam can even be considered.
Relax. PMI does not want you to fail the exam. But they also don't make it easy. PMI primarily wants to ensure that you have grasped the best practices captured in the PMBOK Guide so they fine tune their exam to ensure an acceptable pass ratio.
There are still a few formulas to be learned (mainly in the cost management area). Some students report that they saw no formula based questions at all on their exams and others say that they were really, really glad that they had studied the formulas so in-depth. You should therefore learn the formulas and their applications, and then, before the actual exam starts, write them down on the scratch pad that will be provided in the exam room. You want to do this before beginning the exam so you won't have to dredge them from memory in the midst of an anxiety attack.
Don't hesitate to go back and change the answer to a previous question. You will encounter the situation where answering one question provides you with further insight into a previous question.
Study hard, read a lot and practice many simulated exams until you ace every one will help you pass your PMP Exam.