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Dear Rishabh, first thing is remove self doubt and believe in your self as you have excellent academic record and studying from prestigious BITS Mesra. Through your question, I can make out that personality and communication wise, you consider your self weak. To enhance that, take care of grooming aspects like dressing, general awareness, good spoken English etc through some coaching center or by your self.
Give yourself enough preparation time for pre-lims and mains and do not take it easy. As per statistics, approximately 2 lac candidates appear for pre-lims, approximately 30,000 qualify for mains, approximately 2500 are selected for interview and finally approximately 900 are selected for IAS, IPS, IFS & IRS.
let's consider that you fail in final interview, even then it will be great achievement ans based on your preparation, scoring above 99 percentile in GATE should not be a difficulty and which is good enough for you to get admission in one of the IITs.