One must study without thinking of marks or dreaming of having brighter future in terms of good job etc. We study not to earn money, we study so that we can understand surroundings, know about our past and get some suggestions to move forward in future. Not alone, but along with all of our friends and family, our society.
We need to become a proper human being. Thats why we study.
So leaving behind the tension of getting good marks, study only to learn. I am sure it will help.
Good luck in your life.
Gargi