You can become a Christian and join the Catholic Church, and I encourage you to do so! You have concerns about your family that are probably at least somewhat justified, but the thing to remember is that there is a difference between a secret and something that is private. You probably shouldn’t keep many secrets from your family, but at the same time you are allowed to keep certain things private.
If you’re in college it means you are probably an adult (18+ years old), and the decision is yours alone. You cannot control how your family will react, and while I would not advise somebody to hide their faith from those they love, or deliberately deceive anyone, I also don’t think it has to be something you confront them with if you think it will cause problems. I know it can be hard at your age to separate your life from that of your family, and there is a tendency in most children to want to talk to their parents about most aspects of their lives and share the things they are happy about. Family is important, and it’s natural to want to share with family, but there will be aspects of your life that can belong just to you, and don’t have to concern anyone else. Your relationship with God is ultimately a personal one, and you owe it to yourself to make sure that relationship is the best it can be, and in the way you feel God wants it to be. As a Catholic, I certainly believe that the Catholic Church teaches the best way. I have studied the teachings of other religions and I have always found the Catholic Church to be the most comforting and the most true.
Someday you may decide that your private religious beliefs are something you’re ready to share with your parents. Right now, you probably are not very well equipped to get into theological debates with your parents on matters of Christian faith, so whatever you decide, I suggest you spend more time learning about Catholicism, going through RCIA, and studying the Bible. When you have converted, and have learned more, then perhaps it will be time to talk about religion more openly with those you care about. At that point you will be able to defend your beliefs better, and clear up any misconceptions they might have. It’s also possible the day never comes that you feel comfortable sharing this aspect of your private life with all members of your family. That’s okay too. There are members of my own family that I avoid certain subjects with in conversation, and that’s probably true in every family and in every friendship.