I would relax, because I don't see that there is anything wrong with your personality. Were all different. Some of us can be quieter than others. And the way we act changes a lot in adolescence. My brother, for instance, was a very quiet child, very shy, up until he entered high school, at which point he became an overtly sociable person. If you find yourself spending a lot of time thinking and/or worrying about this, then why not try some anxiety relieving techniques, such as deep breathing, or do something that is calming or distracting to you? [like reading a book or listening to music?]

Hope you're doing alright.