@Liaaa,
A tutor - as fresco says - either someone recommended by your teacher or a friend or someone in your class who you can tell is doing well. And go to your teacher after school one day (assuming you have transportation home) and explain - calmly, nicely, that you are having problems in class and you are concerned about your grade, and would like a tutor. Who would she recommend?
I say to do this because you will not be getting your teacher in the middle of class when she may be stressed - hence the rudeness. And any teacher who cares about whether their students succeed will respond positively to a student who asks for help and has a good idea of how to get it.
My other suggestion to you is to read.
Read a lot more than you think you need to.
True story: I had a ton of trouble in chemistry in high school. My father, an engineer, told me to read the school book from cover to cover. Never mind if we were up to a particular chapter or if we were going to ever cover it. Just, read it.
Now, it's over 40 years later, and I can say with absolute certainty that I don't remember chemistry, and I didn't use it after I graduated college, but I passed. And reading the book helped A LOT.