Can I Restrict My Students Acces to the Lessons?

Yes, you can.

Firstly, you can remove any of the courses you've assigned to the class. If you unassign a course, they can no longer access it.

Additionally, you can restrict access to individual lessons & quizzes by going to the Settings tab in your class and activating the "Restrict Lesson Access to Tasks" setting.

After this setting is activated students will only be able to access lessons & quizzes when they have been assigned to the student via the tasks feature, and only during the tasks active dates set.