Before you start studying Calculus you may want to brush up on Algebra, Geometry, and Trigonometry because your knowledge in these classes will be important when you take Calculus. Not to be harsh, but if you got a B- in Algebra then you may want to rethink this decision because you're far from "real" mathematics.
I agree with Totalderiv, but you should also know why you didn't do well in Algebra. I got a C+ in HS Trig because the HW was 30% of the grade. I also didn't do well in my first semester of physics at college because I hadn't done any math in 9 years (because I kept getting bumped into lower math classes in HS because I refused to do HW). I am now doing fairly well as physics major. So did you struggle with the material? Did you have a personal issue with the professor? Did you party too much?
An intuitive feel for algebra, geometry, and trig is imperative in upper level math. If you had any trouble understanding the subject, being a math major will be painful. There are a number of other majors that include a lot of math if you enjoy it but struggle with it.
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