Hi,
As I see, a lof of students of English have ever experienced this. Me, too. What you should do to overcome the shyness of your speaking English is to do it regularly, to practice it no matter how many mistakes you will make. After that, you will go through another stage that you can realize what mistakes you made and how you can deal with those later. In fact, we all learn from our mistakes. We cannot be good without making our efforts. All I want to tell you is that it is important to keep on speaking what you want and anytime you feel it is right to.
And, at the beginning, maybe you should try to converse with your friends to become more confident. Do it regularly and try to find your mistakes by noticing yourself or ask your teacher or friends to help you with those. I am sure that your speaking will be wonderful.
Have a nice day!
Kounila