How do I master chemistry, physics and biology?

[Hareez]

I am 17 years old, I feel so depress today because recently I answered wrong a lot on my test paper especially in Chemistry.. I entered a class that for me was really competitive with full of intelligent student, for me, i'm not that intelligent, but I try so hard to be like them for my future, and I've made it, for the first time I've got good results in my test and i'm felt very proud and grateful, because of this result I have to enter that class, in that class, I felt that i'm the stupidest in the class, besides all the subjects that I have mentioned, I also need to study another 6 subjects and that is really stressed me. I want an answer from someone that really can help me change myself because I do not want to miss the lesson of the subjects and at the same time wanted to master all the subjects mentioned. Please someone help me give tips in studying this subject, or even the steps about how to make this subjects fun. I need a really honest answer and it will be better if the master of physics, chemistry, biology can teach me the tips how they get great marks on their test.