Lectures are way ahead of the planned schedule for the course. What should be done?
Generally, when a course is assigned a certain number of credit hours, that means that students (and professors) can expect a related number of contact-hours via lecture, tutorials or labs. Your students and dean will likely be upset if you cancel classes for next 3 weeks. 

If you don't want to introduce new material, there are several things you could do.


Review material or go further into depth 
Have students work on their projects 
Have students work on homework or small projects