I don't think I will be able to score good marks in JEE and get admission in a good University as i am not that good at physics and chemistry....will it affect me while learning CS subjects and applying to tech jobs?

No

Many universities have their own entrance exams. Try making a list of universities you want to/can go to and study for those?

It definitely does help to be in a higher-ranked place because you get better people, better professors, better facilities, more funding, etc. You can definitely succeed without one or many of these though, it just becomes harder.

Man that's where I was 6years back. (I was average at Physics but absolutely sucked in chemistry, so bad that couldn't answer a single chem question in JEE Adv)

So I went to a new tier 3 private college (we were the second batch), kept my head down and focused, and landed the first job in the third year.

In engineering, especially CSE in India, it doesn't matter which college you go to. Yes, Microsoft and Google will come for campus placements in select IITs and BITS, but rest all are same.

Grab your sack and STUDY THE FIRST THREE YEARS. Amd work on communication skills (yes boring online lectures on what to say and what not). On the fourth, you'll be partying all day with 8 job offers in hand.

@sudo-compile thankx for the reply maan! I will surely work hard to join my dream company "Google". Well where do you work now?? Just curious

@Tiku I have my own company today.