I go with just knowing a little about the systems but I have the memory items and limitation memorized. While I'm there I focus on system details and review the memory items and limitations about every other day (there on flash cards, takes less than 30 min to review). I don't worry about the flight profiles until about 2 days before the sim training starts.
The stress associated with training are almost always self induced. Have confindance in yourself and work hard. You'll do just fine.