First off, congratulations! Awesome job scoring the internship!

Second... These things take time adjusting to, not going to lie. I felt the same way transitioning from retail (grocery store) to working as a temp. Office Clerk at the college I attend. In the end, I loved it so much that I didn't want to leave, and I'm hoping that I'm hired again next summer.

Just remain calm, take a few breaths, and think positively! Think about how many people who would probably love to have that internship.