Breathe. :) Keystone exams are end of course proficiency exams - they are meant to measure if you understood the point of the course. They don't require perfection. Like you said, you have plenty of time. If you don't achieve a proficient score your first go, you do get more chances: Students who do not pass the Keystone Exam score must receive remedial instruction and must retake the Keystone Exam until a passing final course grade is achieved. After two unsuccessful attempts, students will be eligible to demonstrate proficiency through the completion of a project-based assessment that will be scored by a team of regional teachers.

But the point of keystones are to show that you have passed the class. If your homework, quizzes, and tests are passing, you will likely do ok in the Keystone test if you study.

I would encourage you to speak with your teacher after class about your concerns - they can give you specific advice on where you can best focus your studying.

Good luck!