How to think positive?

i am a college student. i was among the toppers in my school but during the end years of my schooling everything changed. the graph my academics keeps on rolling down even now. on the other hand almost all the other friends of mine is doing great work today. this makes me more sad that i m scoring much less then those people. i cant study with this thing in my head. i dunno its stress or depression but it is really pissing me off. does this means i m a failure?