I think you are mentally pressured by your family.
Try to consult your counselling teachers or your form teacher.
Try to reason it out with your parents, tell them how you feel. Let them know that you already had done your best. Talk to them about what you really want.
If you can't face them alone, try to get help from your counselling teachers or your form teacher. The best is that with teachers who are more close to you.
If it doesn't work out well, just try to ignore those harsh comments. Don't put them in heart.
If after they had scold/blame on you, you could always find someway to ease the pain in your heart.
For example, chat with your friends, or do something you like most,
You can release pressure on doing exercises, drawing, singing, listening to music, or watch tv.
Sometimes, when parents are obstinate, you cant do anything to change it.
When they blame you for something, Just speak the truth, to believe or not to believe is up to them, be proud of yourself because you are honest, if you get punish, stop thinking that you're being punish,Think the other way round, enjoy what you are told to do.
For example, my parents never ground me.. I just love staying indoors knitting, games, songs, reading, drawing etc.. its enjoyable.
If your parents, does not satisfied with you results, Let it be, TELL THEM YOU HAD DONE YOUR BEST AND FURTHER BLAMING OR PRESSURING WONT DO ANY GOOD TO YOU. YOU ARE A HUMAN, NO ONE IS PERFECT INCLUDING THEM. YOU ARE YOU, YOU ARE THEIR DAUGHTER AND NOT SOME FREAKING ALBERT EINSTEIN.
If you had been honest all the time, and had done your best. You had nothing to feel sad about. Just take things easy and live your life, your way.
hope that helps....