Here are some tips for you to overcome exam anxiety and gain confidence:
Take a piece of paper and write down exactly what you are scared of. Try to be as specific as possible. Fear of failure is usually one of our most prominent fears. Make a list of the events that you think will ensue if you fail. This helps you to be more confident because you realize that you are now prepared for any consequence.
After you have written down your fears, define what you mean by success. Is success to you passing exams with a B Grade, or coming first in your class or school, etc. Now you understand that your fears are actually driven by your desire to succeed and you will also realize that most of your fears are based on your perception that you have not prepared adequately.
Now that you have defined your success, you will realize that there are only 2 factors behind your fear; a) A perception that you are not well prepared; or b) A perception that even while you have worked very hard you will still not succeed. Both these perceptions can be addressed with better preparation. In the case of perception b), you can overcome that by following a two-pronged strategy. Firstly, identify a tutor who can act as your guide and give you frequent and meaningful advice to correct your weaknesses and build your confidence. Secondly, join a group of students who you consider are at par with you, and compete with them. The more you compete, the more you will overcome your fears. Combine the two and you have a winning combination to build confidence and increase your chances for success.
Identify adults in your life who can inspire you to greater achievement and seek their counsel and support for doing better. The more encouragement you get from those around you, the better you will do in building your confidence.
Michael Phelps, the greatest swimmer ever in terms of number of Olympic Gold medals, took 15-20 minutes every day to visualize his success. This visualization took him through the process of swimming in a competition and how he would beat the competition and how he would feel when he won the competition. This visualization process never included any thoughts of failure. It will help tremendously if you built a similar routine in to your daily schedule.
Finally, do a bit of yoga every day to learn how to handle yourself while under pressure. If yoga is too boring for you, do a solitary sport such as running, swimming, etc. The extra exercise will help you regulate your breathing better and improve your confidence. It is important to regulate your breathing and take deep slow breaths to reduce any physical symptoms of anxiety.