One of the biggest differences between high school and college is that college students are expected to spend much more time outside the classroom learning the material and working on short and long term assignments. If you are a full time student, you should expect your studies to be a full time job. If you want to excel, then your work week may exceed 40 hours of academic work. The quality of your education is determined by the effort you put into it.
A good rule-of-thumb is that you should expect to be spending an average of at least two hours of work per week (including class time) for each credit you are taking to earn passing grades, and three or more hours per week if you want to excel. Obviously, if you find a particular subject easy, you will be spending less time on that subject and more time on subjects you find difficult, this generally all balances out in the average. The minimum full-time course load is 12 credits (3 units), which translates into an average of between 24 and 36 hours spent on academics each week. If you take 16 credits (4 units) then you can expect an academic work week of 32 to 48 hours including class time. Your study load will probably not be steady throughout the semester; it is likely to be heaviest around mid-term and again at the end of the semester.
Spending more than 40 hours per week on academics sounds like a lot. However, assuming that you need eight hours of sleep each night, you have 112 hours that you are awake each week. There will still be plenty of time to do things other than study.