This question crosses the mind of many aspirants when they somehow fail to score what they expected: "Should I prepare for one more year?"

Though there is no simple answer to this question because investing your 1 year is a big thing. Other than your preparation point of view, you may have to think about your personal situations, family support, etc.
To answer this question for you, I am assuming that there is no personal problem in your life and your family is fully supporting you in whatever decision you take. So as far as preparation part is concerned, there is a very simple way to find the answer of this question. Just ask yourself these 3 questions:

Question #1

Do you think you failed in giving your 100% efforts for about 8-10 months?
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Question #2

Did you feel under-confident while writing GATE and felt you could have prepared better?
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Question #3

Do you think the mistakes you made could have been improved if you practiced more questions?

Out of these three questions, if your answer is 'YES' for at least 2 questions, then you can consider preparing for 1 more year.

You may go for self-study or online coaching, but whatever you decide, I would highly recommend you to take a good question bank and not depend on previous year questions only. Any amount of practice will fail if you have not solved quality questions. We have put in enormous efforts is curating such a question bank which will broaden your concepts and push you to think more. Attempt 1 Free test of this question bank: https://exergic.in/question-bank

All the best!