Hi!! Is there a way to improve?

Hello(Hallo) ^^ My name is Melody(Ich bin Melodie)

I'm currently taking a German class in high school. I'm in German II, preparing for German III next year.

I'm kind of nervous to take German III next year because I heard that 60% - 70% of the shool year is only in German. I feel like I don't know enough German to take that class next year. I'm barely passing the German II class with a 74%(anything below a 70% in my school system is consider failing, so I'm nervous that I'm not going to make it...I'm almost at the failing mark...).

I want to find a way to improve my German. Is there a free learning website(besides about.com) or some books I can buy that will help me improve?

Thank you for your help!!(Danke!!)