Science

Greetings from Shiksha.
Kindly visit this link for Best Private Institutes in Delhi for doing B.Sc:
https://www.shiksha.com/science/colleges/b-sc-colleges-delhi-ncr

Dear friend,
SRK University's degree is approved by UGC (under Section 3 of UGC Act 1956).
So don't worry. It will not create any problem for a govt. as well as central govt. organization.
Without any fear, you can go for SRK University.
Thanks.

Hello,
Its a common conception that math is always tough :P
But, if you are interested in joining medical related courses or biotechnology then you must study biology. But you will be eligible to engineering courses as well.
If you choose C.S. you will be restricted to join engineering. As you say you are well versed in maths, I suggest you can take math+bio as your combination as the career & variety of courses will be wider.

Not at all. Maths is not a per-requisite for a course like BCA. Yes, you'll get few mathematical subjects which needs you to calculate but then you'll be taught how to do them. So Maths, wont be a issue with BCA. Anyways, it depends upon Syllabus to syllabus.

Yes, you can go for B.Sc in nursing. No problem in that. It has very good opportunity and wider career prospectives. Admission will be based on your 12th score.

You can do many things such as -
start your own business (for your information most successful businessman are less qualified than you).
continue studying (I recommend that you exercise this option) - If you want to study, please refer my answer to this post.If I got low marks in 12th less than 60% where should I go?
look for a job - search internet, I am sure you will find something
any combination of the above options: like (1 and 2), or (2 and 3) or (1 and 3).
All the best.
Do well in life (this is not the same as scoring well).

BFIT Dehradun is affiliated to Uttranchal University. For more details of the institute, you can refer to the following link:
https://www.shiksha.com/college/bfit-group-of-institutions-dehradun-24049

As per your interest, this would be best. If you like, you may join Engineering Physics for B.Tech program.