These kinds of exam anxiety are common and happens to be before exams.

Keep yourself calm & composed

Be confident about your preparation & believe in yourself

Avoid stressing yourself before the exam

Do not discuss with other students at the last minute about the JEE Advance syllabus

Avoid over studying the day prior to the exam

There is nothing to fear about. That exam is not the end of the world. It's a common issue to be nervous before any big exam, but fear, nah. Never fear any exam. That will only demotivate you. Watch a good movie if you are feeling pressurised. Don't study all day long. take some breaks and spend time with family members. Go out and take a walk. These things will refresh your mind.