I know that you are excited and proud of yourself for taking the next step in your education and beginning your adult life. The next five years are going to move very fast, although some of the days will seem slow.
Trust your gut on who will be a true friend and who won't - most of the time, you're right. Just because your friends think someone is cool doesn't mean you need that person's friendship or approval - a small, tight circle of friends is more valuable than being a social superstar. People will surprise you - people you underestimate now will be some of the best friends you'll ever have, and some of your favorite high school friends will drift away. You wouldn't believe it now, but you won't miss them. When your high school friend invites you to his fellowship's large group worship, GO. You'll find your brothers and sisters there and wish you'd gone sooner.
Focus your energy on the people and activities that give you energy rather than the ones that take it away. Your roommate is right when she tells you not to take on too much. As time passes, you will begin to identify more and more as an introvert - yes, you like people, but you need quiet time to recharge.
Your easygoing nature will lead some people to absolutely adore you - especially people who need a little extra attention. Remember to keep your guard up, maintain boundaries, and not take advantage of others' feelings for you. By the way, that thing you do when you don't want to hurt a guy's feelings by dumping him so you start acting like a lunatic so he'll dump you? Not doing anyone any favors.
You will always want to live your life ten times, ten different ways. Don't waste this one.