If you are preparing for the first time, skipping a year completely depends on your confidence and preparation level. If you think you're not ready, you're probably right. After all, it is not an easy exam by any means, and it takes a lot of practice and dedicated hours of study to ace and secure a good rank.
It completely depends on you and your goals. If you are confident and ready to appear in the upcoming JEE exam and score well, then nothing is better than this. However, if you feel that you need some more time to prepare and gain confidence, then you should definitely give yourself that opportunity without any guilt.
If you have attempted JEE Main before and failed, next time it will be easier for you if you skip a year. This is because now you will not have to worry about school exams and other preparations. This is also applicable for first-timers who decide to take the drop year.
If you have cleared JEE Main and failed to clear JEE Advanced (or did not score the desired score), you will have some more time to revise and practice, one last time to achieve your goal There will be confidence.
If you are determined to achieve your goal then revising for one year for JEE preparation is not a waste of time. You must have the willpower to study the same book and read the same questions again and again.
Taking a year off is a tough decision but it will lead you toward your dreams and make your parents proud. If you give your best, you will always feel confident whether you get selected for JEE or not.