Try the other side of the what if's...that is, what if it works out better than expected? What if I learn so much that I'm eager to learn more? What if the co-workers are the finest people that I've ever been around? What if the HR folks are so accomodating that they'll work around my school schedule because they like me so much?

Remember, when you're in school, nobody generally has the experience in their field of study. Everyone starts at the entry level. You'll do fine. Seize the day!