those who demotivated that you will fail or not get good mark how to cope with them
Rohit, there will always be people who will demotivate you or try to bring you down no matter how successful you become. It is just a part of life, the ones who accept it as a part of life and turn those demotivating words into a reason to achieve greatness are the ones sitting at the top. If you think you are good enough then no one, I repeat, no one has the right to say that you are not, you just should not let anyone dictate you and tell you that you are not able, if you have confidence in your abilities then opinions of other poeople should not matter. Just keep working hard, believe in your abilities, turn those harsh words into a reason to fire yourself from inside and most importantly choose your guides cautiously as critics( healthy critics) are also important to keep you on track.
Good luck and keep working hard because that is the only thing that you can do, as they say "control the controllables".
