Advice from someone who has been tutoring Calculus I, II, and III for three years:
If you are about to take a Calculus I class, and you feel nervous at all about it:
I say this with all the love in my heart. I know it's common to joke about always forgetting everything you've learned over the summer. Thing is, if your college major requires you to take any level of Calculus, you will need Algebra more than anything. Please review. You WILL feel stupid in class if you can't remember Algebra and basic arithmetic. (I promise you, though: you are not stupid. Don't give up before you start. I can go on forever on that, so I'll spare you for now.)
Specifically, review these:
Factoring a polynomial (an equation that looks something like x^2+x+1, though with different numbers)
Quadratic formula (I know you hate it. I don't care. Review it briefly.)
How to factor in general (Example: 4x+2 = 2(2x+1). Don't remember why? Review it.)
Dividing and multiplying fractions (Please review this. I beg you.)
Exponent rules (Again, I'm begging you to review these. There's not that many.)
Understanding the difference between y and f(x) (Hint: unless you're going further into math than Calc I and maybe II, the difference between the two is ultimately nothing to you)
How to find the equation of a line between two points
Slope of a line (Does "rise over run" sound familiar?)
Trigonometry. Just the basic stuff. You really don't need much review here, but look over it briefly at least to understand what's going on.
UNIT CIRCLE. If you don't know what it is, look it up. Memorize the top half of the circle. Ask for help understanding what it is. Watch YouTube videos about it. Please. Depending on your professor(s), it can help so much. You might only need to memorize the first quarter of it. There are patterns to it, so it's easier to memorize/understand than it might look at first. Believe in yourself.
Anyway, that's all I can think of off the top of my head. To anyone who reads this, I hope it is helpful.
If you're scared of Calculus, take it from a tutor: the concepts are simpler than they sound, yet I completely understand whatever frustration or confusion you may feel because of Calculus. Math becomes its own language at higher levels, and learning that language can take a lot of time. You can still do it. You're not dumb for struggling to understand a language you haven't fully learned yet. Have patience with yourself, and take the time to try and figure out how to translate that language to phrases and words that you're more familiar with. You'll do just fine.