Dear Sneha
If you are willing to become an astronaut you need to have self confidence and also self motivation too.
let's think that if you are a astronaut, you don't know how your life will take you.. And it's like you need to spend so much time in the office itself... That's why I said you need both confidence and motivation.
Coming to the topic what you want to follow to become an astronaut,  click on the below link :
ASTRONAUT All the best.

Astronauts can be biologist, Doctor, engineer, Pilot but,  mainly engineer or pilot. You can do Btech or Mtech from IIT or other colleges in aeronautical or mechanical engineering ( best is IITs). You apply for NASA by checking and they will tell you further.