NIT

Writing CAT is the first and foremost thing. After that apply for each and every IIMs and IITs based on previous year's data.

IIT-Kharagpur and Delhi are the best IITs and National Institute of Technology-Tiruchirappalli, and National Institute of Technology-Karnataka, Surathkal are the best NITs M.Tech in mechanical engineering.

Masters of Computer Applications (MCA) is known to be as one of the popular course among aspirants to build their future in IT Industry, because of the vast career options that this programme holds. It is a three-year PG course in the field of computer applications. The programme's main focus is on the development of latest applications with the help of various programming languages. Check out the article below for more details:
https://www.shiksha.com/it-software/articles/top-mca-exams-in-india-blogId-13629

Bachelor of Architecture: Eligibility The duration of the course is 5 years and to get admission into B.Arch. the student must be fulfilled the following conditions: 10+2 or equivalent with minimum 50% marks along with compulsory subject of mathematics. 10th + 3 years Diploma in any stream from a recognised university/ board/ institution. Cleared NATA (National Aptitude Test in Architecture) with the 80% marks conducted by Council of Architecture.

You have enough time to prepare well. Nudge yourself and study properly to get admission in NITs or IITs.

Sorry, that is not possible as NITs don't have admission procedures other than JEE Mains window.