There are two different issues here. The ability to speak up to your parents is one issue. The ability to study in the way that you need to is another. The issues overlap but are two distinct issues in my opinion.

In general with regard to your speaking to your parents. A main way you can build confidence is by getting some experience with speaking up. It is a chicken/egg, Catch-22 problem: you need confidence to speak up, but you get confidence from speaking up. Still, you need to start somewhere.

You could start with "small" things. "No thank you, I do not care for more food." "I am going to the store now, not in an hour."

It is not going to be easy to go against their wishes, even in small things. But small things could be a good way to start. Start with the smallest you can think of.

With regard to the distinct issue of how to study for your exams: I am not optimistic that you will actually get anywhere by bringing up your stress or how you hate the way she is acting. I'm sorry to say that, but here is how I see it: the exam is a short-term issue. Her behavior is a longer term issue. To do your best on the exam, you need to be able to focus on that, rather than to devote yourself to a longer-term project that will involve engaging her on the bigger issues. Therefore, my suggestion is the following:

"Mom, my studying is under control."

Repeat as often as needed. You could vary the words, but not the message.

"I am following my plan."
"I have it under control."
"I am on track."
etc.

If you are able to leave the room and thereby end the conversation, do so.

When you say that you are not okay, what do you mean? Do you feel suicidal now?

(((((connect.the.stars))))) (((((connect.the.stars)))))