CAT

CA and CAT both are nowhere related. But, it would be helpful if you finish it first because the CA tag will give you additional benefits during selection and placements.

With this percentile you won't get any good college. Reappear next year for the exam and score well.

You will get a call from every good college except IIM-A and B with this score. Your B.Tech score might be the reason for this.

I am not too sure. CAT cut-offs are around 85 percentile, I guess.

CAT is held in the month of November or December every year. There are 3 sections in the paper comprising of Quantitative Aptitude Verbal Ability and Data Interpretation and Logical Reasoning. CAT is accepted by IIMs and other top B-schools for admission to their PGDM/MBA programmes.

If you have a below zero percentile in Quants you will have to explain it in the interview also, some colleges may not give you a call because of the negative marks.

85+ percentile will help.

You can apply for TAPMI, IMI-Delhi, SIMSREE-Mumbai, LBS-Delhi, IFMR, Great Lakes, IIT-KGP/Roorkee/Kanpur/Madras, K J Somaiya. The application forms of these colleges are still open, you can apply to them.

I don't think you'll get scholarship but you can call them and ask them about your case.
Scholarship criteria in Amity:
100% Scholarship Eligibility - Students securing 93% aggregate and above ((excluding Physical Education/ Fine Arts / Performing Arts / vocational / non written subjects) in CBSE/ ISC Board of Class XII and 80% in Graduation.
50% Scholarship Eligibility - Students securing 90% aggregate and above (excluding Physical Education/ Fine Arts / Performing Arts / vocational / non written subjects) in CBSE/ ISC Board of Class XII and 75% in Graduation.

You should prepare for SNAP and CMAT as they will provide you with more chances of getting into a decent college, but don't forget to appear for CAT as it has the widest spectrum of colleges.