Hi Carolin,
Replying because I thought you might benefit from a complete beginner`s experience to a retreat.
A couple of years ago i signed up to a 10 day Goenka-style vipassana course, after just googling "meditation" and reading a bit about it . In the couple of weeks before it i only did a couple of 30-60 minutes sits and that was my whole meditation experience before it. On top of it i had (still have) a bunch of social phobias and a few "what did you just get yourself into" moments.
Somehow all my worries washed away once i got there. I didn`t do great in terms of progress because to be honest i didn`t know much of what i was doing and i was just discovering a new method. But i felt great, didn`t have any problems with sitting 10 or so hours a day, and the "noble silence" rule took care of my social phobias. If the opportunity would present itself, i would do it again.
I am sure you will do great. Don`t burden yourself with worries (or do but watch your self doing it), probably just the ego fearing for its life.