What do I do if i have a failing grade?

At my school, everyone thinks grades are not important. Well, I do! I'm just a freshman, and my grades turned from Straight A's, to straight B's, to straight C's. Tomorrow, report cards are coming in, and all I know is that I have an F in science, a C- in english, and a D in math. What should I do? My grades are getting worse, and my mom is already going berserk! Please help...