Can I graduate High School?

I got to Manatee School for the Arts in Palmetto, Florida. I am a Senior, and I am extremely smart. I don't mean to boast or emanate arrogance, but I'm very Intelligent and was even voted "Most Intellectual" in my class. However, I have slacked these past High School years. I know I've gotten some low grades, but I didn't think my GPA was so low that now I'm in danger of graduating. I have the highest ambitions of becoming an author, and I don't want to let myself, my family or my girlfriend down. I received a letter today from my school that said I'm in danger of not graduating this year due to not maintaining a 2.0 GPA throughout my High School career. Now, I don't honestly know how it could have been so low this entire time, also, why am I being informed now? In the middle of Senior year? And finally, why hasn't anyone brought this to my attention in the past three years? I'm very scared. What would my girlfriend, or my mother think of me if I failed High School? I don't want to be a failure. How can I even fix this? How can I fix it now if I was supposed to have maintained a 2.0 all of High School? Is there anyone who can help me sort this out? I'm having a melt-down. This can't be where my future is just suddenly cut short.