I am a failure

Well, I feel even more pathetic writing to someone I've never met about my problems. Anyway here is why I am not enjoying life: My sister is a freshman in college, and she is soooo smart. She gets perfect grades, and everything just comes so easy to her. She is actually taking sophomore classes because the freshman ones were too easy. But me, I am just in High School, a lousy sophomore, and I'm a failure. I mean, this semester, I am taking Adv. English 2, AP World History, Adv. French 2, and Adv. Algebra 2. I am so overwelmed and so stressed that its unbelieveable. I'm making A's and B's except for in my Adv. Algebra 2 class. I have a 69% right now. My parents say that they never compare my sister and I, but how could they not? I do, and it makes me feel worse. All my friends are pretty much getting staight A's so I feel so stupid. I always have so much homework and I never have time to go outside or play with my dog, or do any of the things that I enjoy. My dog seems so lonely and sad, that I just can't stand looking at her poor puppy eyes. I'm trying to bring my grade up in math, I'm starting to go to tutoring, I take notes in class and pay attention, but nothing seems to work, and the teacher is not understanding at all. He doesn't even care. I go home and cry a lot because I'll never be able to bring my math grade up. I am constantly feeling misery and hopelessness. I am so stupid.