Who am I really?

I feel that since I have been keeping my self busy, I have become more and more stressed out. I moved to a city, work part time and am a full-time culinary student. I feel that my time is spent stressing out to do well, when in the end I have been doing well all along. I worry about getting good grades when I already have great grades. I worry about being on time when I have already arrived early. I worry about money when my wallet is full. I don't know if this is normal for a 20 year old girl. Often I think of older adults that say to me, "Oh I wish I could be twenty again!", and I feel that I will never have the opportunity to look back and say that. Am I missing out on the prime time of my life?