Introversion is nothing to be ashamed of.  Having a small circle of confidants is the universe showing you that you have no upperclassmen or pseudo-friends to impress, just people to love.  Being calm and focused while the world around you is so frantic and showy can be intimidating, and taking a break to close your eyes and breath is perfectly normal.  It doesn’t have to be as complicated as we make it.
Having a quiet voice is an asset.  When someone who is usually an observer speaks, the room becomes quieter and people start listening.  Your volume is not a reflection of your content, and your words are quality over quantity.  When you are comfortable to speak, do so with poise and confident diction.  You do not need to be loud to be heard.
Thinking before speaking is a skill that you possess naturally.  You analyze your sentences and voice them when appropriate, and if the topic changes or you are not ready to speak you are fine with staying silent.  If people tell you to speak up or say that you never talk, tell them to listen more.  Communication is a two way street, and extroverts need to understand that introverts process internally, and introverts need to understand that their silence can sometimes be misconstrued as disinterest.
It does not matter whether you are quiet, loud, or somewhere inbetween.  Whether you prefer low-key conversations or exciting parties determines only what you do with your Friday nights.  The amount of friendships you have is irrelevant to who you actually are.  The popularity contest ends after high school and then all you will have is your honest self.  Your Facebook friend count will not impact your college applications or yearly salary.  Being friendly and open is important, but draining yourself to exhaustion and pretending to be extroverted will only draw you further from yourself.
Just be who you are comfortable being.  It takes time to accept yourself and learning your limits is necessary in figuring out your personality.  Try being loud, try being quiet, settle somewhere in between until you feel grounded.  Having two feet firmly on the ground is essential before you can even begin walking.