BCA

Sorry, I don't think you're eligible for VIT. They require a candidate to score at least 70% in +2 in order to be eligible. So, you can't pursue BCA from VIT. But there are many other universities which will get you admission. You can try Christ University Bangalore, which is also considered as one of the best universities for BCA candidates.
If you want to learn programming languages which you will be studying in your BCA course then you can check out this app "BCA - Course Programming" which is specially designed and developed for BCA students and is available on Google Play Store. It has programs and assignments of languages like C, C+ and Java with their outputs. You'll be studying these languages in your 3 years of BCA.

Yes, you're eligible for both universities. Your +2 percentage is good. But both of these universities select candidates on the basis of entrance exam and personal interviews. So, you'll have to prepare for that too. Entrance exam will include logical reasoning, grammer etc. If you want to learn programming languages which you will be studying in your BCA course then you can check out this app "BCA - Course Programming" which is specially designed and developed for BCA students and is available on Google Play Store. It has programs and assignments of languages like C, C+ and Java with their outputs. You'll be studying these languages in your 3 years of BCA.

It depends that how less the marks really are!
You can still find out colleges that do not require high percentage as eligibility criteria for taking admission in M.Sc maths. Scoring less is not an issue, a number of colleges provide admission even though a candidate has less marks in previous qualified degrees. You find out more about such institutes which invite applications for your desired course. Go to their website, if the college is in your hometown, visit the same. Or else call on the toll free numbers of various Universities and enquire about the eligibility criteria as well as admission procedure.
I am sure, you would find one. However, yes, work hard this time and fetch good marks in M.Sc. As you know, the graph should go upward as you proceed further with your career, as this will justify your performance and seriousness as a candidate for job or so.