How to be a person who always satisfied with what she has? ?

i am one of the students who has been included in the dean list in my university. i am very grateful with my result. but the problem is, i become overconfident and always want to be the first. every time my marks for the quiz a bit lower, or i didnt perform well in exam, i will be very sad and sometimes i could not accept the fate. im also a participative student in my cl, i always ask questions to my lecturer, and it makes me to be well known to my clmates. im afraid, if i cannot achieve the highest mark, my friends will be saying something bad to me. help me to calm myself down...