It may seem like your world is closed off from time to time whenever someone looks at your life from an outside point of view. You may be seen as someone who's antisocial or a "hermit," but that's okay.
To yourself, you know that you have your limits and you prefer to be the person who stays inside, like, on a Friday night. Maybe you like to sit and read a new book or binge watch the latest season of your favorite show. You might even like to study and stay somewhere comfortable where you know that other people won't bother your work. Sometimes you just need to relax and keep to yourself after a busy day of being surrounded by so many people.
But you are not lazy or selfish. You are not any negative description solely based off of your personality or choice to be more reserved and kept to yourself.
It's fine to feel like you want to be home when you're out somewhere and to later feel like you want to be out when you're home. To be someone who keeps to minimal people in a group or no one at all during a party is okay. You do not have to put yourself out there with people who are extroverts to seem like you're having a good time.
Everyone is different in college and being an introvert doesn't mean that you're not worthy of having a good time regardless. Keep to your small circle if it's what makes you comfortable or branch out if you're feeling like it. Don't feel like you have to be overwhelmed to make a lot of friends or have to be someone who's always ready for action.
Introverts can be people who love a good time by going out too, but liking to stay behind by yourself is totally cool too. College is about making choices and working to your own plan, not anyone else's idea of a proper plan to follow.
Never feel ashamed to be an introvert, it's just who you are
As for any extroverts reading, don't feel angry towards any family or friends who may be introverts. It's nothing personal against you but it's just what introverts prefer to do, staying inside or close by home to do things by themselves. An invite to do something together never hurts and maybe offering to stay in for the night with them could offer some fun options like getting to know about their favorite show or what they like to do during free time.