I'm having trouble finding what to do in Summer school?

So I'm currently taking a course in Summer school online and my teacher says I need to be online every single weekday for 5-6 hours. But what I find is that I finish my work within at least 2 hours, and all I'm doing the rest of the time is checking the forums and my school e-mail. What should I do for the rest of the day? I have 4 weeks to complete 18 ignments, 3 tests, and 2 culminating activities. I don't want to go too far ahead and do so many ignments and tests because then I'll really have nothing to do in the long run. If I'm not online every day for 5-6 hours, the teacher might call the online principal and it could get me removed from the course. So what should I do?