I know how you feel, but you are stressing yourself out unnecessarily. The first day of class is VERY laid back. Most of the time you just get your syllabus, talk about the course objectives, and possible start the first section of the course. That is it. Your proffesor more than likely will NOT call on you the first day, unless it is to take attendance. Why would he call on you that day, you haven't had an assignment yet, right? You might be asked to introduce yourself, but you are more than capable of reciting your name and why you are there.
You sound like a very concerned student, and if that is the case you will have no trouble with the classes. Just use your fear of failure to your advantage and work really hard. You can do it.
By the way, not that you won't have to study, but Sociology and English are soooooo doable in a summer course. Sociology, IMO, is very common sense and English is more paper writting than anything else. Good luck, and let us know how your first day goes.