You have asked some very difficult questions; that must be very concerning to you. It is always difficult to leave what is familiar behind and move on to new things. By deciding to do such a thing, you are already on your way to being less shy and having more confidence. Many people would not be brave enough to do what you are doing. Focus on your accomplishments in order to gain more confidence in yourself. Remember that it takes a special person to do what you are attempting to do and to work hard enough to achieve your goal! If you get to campus and are still very overwhelmed, you may want to visit the counseling center. The staff there can work with you in helping to overcome some of your fears.
As for being shy, many people in the US are fascinated by people from other countries. If you want to make friends, you will probably only need to make yourself available and someone will approach you. Also, most large schools in this country have special orientation programs for international students. By participating in such a program you will meet many students in your same situation from all over the world. They may be just as shy as you are, but since you will have a great deal in common it may be easy to break through some of the fear. All schools have orientations for first-year students and transfers. Even if you do not choose a school with a large international population, you have the opportunity to meet other new students in a small group setting.