Larissa, it is a joy to be in contact with someone who has the privilege of obtaining a college education and is open to what God wants her to do with her life. Congratulations!
I’ll tell you a secret -- you don’t have to wait four years to be involved in mission and/or mobilization! When we respond to Jesus to be His followers, He has a mission for us, right where we are! If you haven’t gotten involved in a Christian fellowship on campus, I would encourage you to find one. I would assume that you attend church, but there is something special about meeting regularly with your fellow students who love Jesus and are involved in learning more about Him and participating in campus outreach. If there are several groups, visit them, and participate in one that emphasizes worship, Bible study, evangelism, and discipleship, such as InterVarsity.
Participation in such a group will be helpful in several ways: " You need the stimulus of others who are committed to following and obeying Jesus. " You need to help others who are weak in their faith. This will, in turn, help you to grow spiritually. " As you participate in the group activities, you will learn basic principles of ministry. " As you learn these principles, I think the Lord may begin to talk to you about your focus of service when you graduate, whether it be as a professional missionary or serving as a layperson.
How did I know? Every one’s story is different, of course. Mine is a quite unusual since I am the son of missionaries and from my childhood I felt the Lord calling me to be a missionary. As missionaries visit your church, talk to them, and ask them what their experience has been. You might also like to read some missionary biographies. A wonderful book, by Ruth Tucker, is From Jerusalem to Irian Jaya. It is a history of the church through the short biographies of missionaries. The lives of these impressive individuals will challenge and encourage you in your own commitment. You will discover a wide range of ways the Lord has led people as well as a broad variety of things people have done to serve the Lord.
Your question about your major of theater set design may be putting the cart before the horse. How do you know that the Lord wants you to major in this subject? Usually we major in something that has to do with the Lord’s call on our life, and not try and fit a commitment of a course of study into what the Lord calls us to do. However, my experience is that the Lord is amazingly creative in using what we have learned in the work He calls us to do. Ask Him what you should major in as you are asking Him what He wants you to do with your life.
The important thing is to stay close to Him, grow in the knowledge of Him and His ways, and He will show you the answers to these questions. He tells us that He is “The way, the truth, and the life” (John 14:6). He is the Good Shepherd (John 10), who goes before His sheep. Our first call is to a relationship with Him, not an activity.
Blessings on you as you continue on in that great adventure called a “college education”!