CBSE 12th

Hi,
Yes, you can apply for the course. Candidates must have passed 10+2 with 45% marks in aggregate. Students must apply online. Admit cards (wherever applicable) to be generated at the university website. Regards.

Dear friend,
You are eligible for doing a degree course. You have 50% in your plus two thus your admission is based on the college cut-off percentage and the percentage score in the admission process. The procedures are:
You must register yourself in a university for your degree programme. The university publishes its status and based on its status, you can move ahead with the with degree programme.

Of course, since the closing rank for CS in Presidency is 52000.

No, it's not a wise idea. Go for coaching along with your studies. Both have the same syllabus. A proper mock test will help you get a good score along with your studies.

KCET 2018 College Predictor:
Use your KCET 2018 rank to see where you can get admission at the link provided below:
See the courses, colleges & rounds you may crack
The result is based on admissions data of KCET 2017
Get resources & insights on colleges & courses. Regards. https://www.shiksha.com/b-tech/resources/kcet-college-predictor.

Since you have given improvement for class 12th boards, from now on, you will have to put up your improvement result certificate everywhere asked. The original will not be considered.

https://www.shiksha.com/animation/2d-3d-animation/course/integrated-b-sc-m-sc-in-multimedia-st-xavier-s-college-park-street-Kolkata-281121
This is the link, where you can see the details for integrated B.Sc+M.Sc in multimedia.

If you want to get into IITS or NITs its mandatory to take up JEE. So, I suggest you for drop and go for coaching and appear for JEE. It will help you get a good future.