My teacher said I wasnt working hard enough and I lack giving details in some of my work. Am i a big fat loser?

I do my best but the material is just hard. I did ask questions in all but I still fail. In my last test I got 27 out of 100. In parts of my test my teacher said I lack explaining details. I even did some extra credit to raise up my grade but I STILL have a failing grade. I have a 52.97% in my class and I doubt I'm going to pass it. I ducked up my tests and I'm just done. I'm a huge disappointment to myself and my dad and stepmom are going to be very pissesd off. They are very strict and blunt about education. They want me to do my best. In my other class I got a 79.45% in my class. I gotta study for finals. My critical reading class I doubt that I will pass. Why am I so stupid?! I'm done.