Hi nicolinaa,
Every school arranges timetable lines differently, so it's impossible for us to answer this question without an understanding of what your timetable looks like and how your school has scheduled your classes. Even between schools, things such as period lengths and number of periods in a day varies.
I've noticed that you only seem to be doing 11 units, which is strange since prelim requires a minimum of 12 unless you've already completed an accelerated subject. But since you only have 11 units, you should definitely have free timeslots to act as study periods. I'd recommend you take a close look at your timetable to see where that time has gone, and to ask your school if you're still confused.
Hope this helps!