Being away from home for the first time meant no one was looking over your shoulder to see what you were doing–and suddenly you had the freedom to do whatever you wanted to do. If you didn't have any strong inner convictions or restraints, that meant you probably went along with the crowd.
I'm thankful, however, that you don't feel good about what you've done–because that tells me God is working in your life to draw you back to Himself. Begin by turning to Christ and asking Him for the forgiveness you need. The Bible says, "Blessed is he whose transgressions are forgiven, whose sins are covered" (Psalm 32:1). And if you've been depending only on your parents' faith, now is the time to make your own commitment to Christ.
Then take definite steps to strengthen your faith. In a few months, you'll be back in the same situation–but will you be any different? Now is the time to answer that question. Reconnect with your church and seek one or two Christian friends who can encourage you and pray for you.
In addition, learn to walk with Christ every day. Set aside time alone with Him through prayer and Bible study. Also, find out now what Christian groups are active on your campus, and become part of one when you return.