Rely heavily upon what you already know about your personal academic strengths, weaknesses, likes, and dislikes. Your past performance is the best predictor of your future success. Don't disregard as trivial the activities that have brought you satisfaction and recognition, no matter how insignificant they may seem. And don't let the shadow of a doubt keep you from making a choice. Remember, some degree of uncertainty will always accompany a tough decision.
Most new students are concerned about succeeding academically.
You know the competition will be tough and the courses demanding. Large classes, teaching assistants, and diverse teaching styles mean that you will have to make some adjustments. You are academically qualified to succeed here if you have the motivation and commitment to do so. Finding new friends will also be important. You will probably have a roommate for the first time and will be concerned about getting along with that person.