CBSE 12th

if you are well determined.then drop otherwise go for private colleges

You need to have completed your B Tech or BE in the streams like electronics, electrical, computer Science or mechanical engineering. You need to have aggregate score of 60% and above throughout your career.
Indian citizens who are not more than 35 years of age can apply; however, there is some relaxation in the age limit for candidates from the reserved categories. The candidate can appear in the written test during the final year of B Tech or BE course.

Any stream of Students do BCA but Computer Science is only for those have select thAt subject with Science stream

Your final report car should not show it Kriti. But anytways you must tell this to your future recruiters if a question arises during interview. It is always better to tell the truth so that your employer knows everything and accepts your candidature inspite of such things. You then stand on a strog platform and are mentally free of the burden.

Many options are there other than engineering like B.sc,BBA,B.pharmacy ,B. com BBM, BBS,etc. Choose one which you like most.

yes there is a bit of chance

Dear parth. almost all the colleges already announced for BBA programme which you stated above. every institutes their own methodology in getting admissions for BBA. if there is a time still prefer alliance that is a good one if you don't get admission there prefer acharya. all the best.

Please visit the following link :
http://study.com/articles/Become_an_Automobile_Designer_Education_and_Career_Roadmap.html