If you are so scared to do something at least try. Do it anyway. Decide to become courageous even if you are not. Fake bravery, nobody knows that you are scared if you act like a tough guy. Some people around you are even more scared, you are not the only one who feels it. Some people cannot even fake bravery so if you can at least fake it... you are one of a kind.
Everyone is scared, there is no such thing as a man without fear, the only difference between a successful man and not is the successful man is acting like a tough guy, he is faking his courage until he believe in himself.
Once you are in the middle of a challenge and you are so afraid to do it, just do it, just try it. There is no harm in trying but there is so much depression in stopping.
When you go home and you didn't try, you will regret the moment that you let escape. "What if I win?, what if I nailed it?" these are the words that will haunt you everyday. Even if you fail, at least you know the result and you will never wonder everyday what will happen if you just give it a try.
Time is running, decide now or quit. If you decide to become brave use all your strength, use all the energy you can use to conquer the challenge. Humiliation, mockery, critics - these are just bullshits that has nothing to do with your life. People who do these things are people who can't even try. Embrace the negative feeling now and let it go or you will embrace it for the rest of your life.