I would talk to my parents about this, or maybe a school couselor. It is not okay that you're suffering like this from the school work.
And like others have said before me, you do not have to be perfect. Nobody is, and nobody will be. You'll only be putting yourself under (too) much stress to try and be perfect. Everyone has flaws, and there is nothing wrong with that.
I dunno if you're just trying to pass or try getting the highest grade possible. If it's the latter, take a step back and go for passing it.
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