Job advice please needed?

So I'm a student going to school working at a retail clothing store. Our store hours are based on our sales. So if the business is doing crummy it will effect your hours for the following week. I've been there for almost 2 years now. We recently got a new store manager. I feel like she singles me out. She's always buggin me about my sales telling me that I'm going to be fighting for my job unless they are higher. Today she gave me my second write up based on the sales. My sales aren't the lowest in the store I'm 3rd from the highest. But one more write up and I'm gone. I want to put in my 2 weeks because I don't want to risk getting fired. I live paycheck to paycheck paying for school rent etc...But I'm also afraid if I quit I'm not gonna be able to find another job as quick as I would like. I dont like the pressure this lady is putting me under? I've never been fired or had any writes up so should i quit or just let her fire me? Good serious advice is needed please thank u