My teacher is giving me bad grades on purpose...?

So I've been doing good in Algebra the beginning of the school year, but a month ago I started slipping and got a D, I got yelled at so I tried getting better. Last week I've been working really hard and got good grades when I graded my homework assignments, but my grandma checked FamilyLink and said that I made no good grades at all in her class last week. Over half of the homework I graded was good!! It also says I am still missing some which I had turned it. I really thought I was doing better... I failed my test, but she's letting me correct it thankfully. But I'm scared about when my Dad finds out!! He said one more missing grade and he will hit me. I'm scared!! He won't believe me when I say my Algebra teacher might be giving me bad grades on purpose. I have the actual assignments with me, well four of them and they are all good, so I will show him. But I'm still scared!! What do I do!? I know she might not be doing this on purpose but I have proof I've been doing really good with quizzes (QUIZZES NOT THE TEST) and homework!! What do I do!?