too shy to function!?!

i'm a junior going into senior year, you can say I am shy when I first talk to people, sometimes I am shy when I talk to family members.I am afraid I will say the wrong thing or I am afraid I have nothing to say so I start worrying and I panic and then have nothing to say. Most of my friends know me as the most talkative out of our group and my immediate family and grandparents think I talk too much. I can talk to Random strangers but why am I shy when I go to school and have to interact do I appear shy? I went on a trip to Ohio with my classmates (on a school trip) and had fun, and was talkative. However once we go back to school I go back to my shy self. I go to public school and my all my friends go to private schools so what is wrong with me? Tips on how to be more talkative all the time would help, is it I have low confidence not having a friend around? Will I grow out of it by college, sites would be helpful and does yoga or acupuncture help? I feel like I could have made more friends in high school, but I didn't because of my shyness:(