You should prepare yourself from the beginning when it comes to giving entrance exams. You should believe in yourself and know that things might change. You shouldn’t stress yourself out too much and just focus on what is in front of you.
Here are a few methods that might help:
Overall, make sure your concepts are clear. Follow the NCERT book to the core and study well. You may have prepared for JEE Mains which will also be a good booster. You should also practice last year’s JCECE question papers as this will give you an overall idea of the exam.