Yeah, I'll second what xiansheng said about the Algebra part. I think the fundamentals of calculus are actually quite easy, it is more or less the algebra that goes along with it that can be a real pain in the butt. It is more or less just trying to remember all the little rules with your trig identities and simplying your answers.
I'm not sure if you do this or not, but for me in calc 1-4, what I tended to do was just find how all the questions repeat themselves. If you think about it, every single problem out there is done the same way in calculus. Calculus is actually straightforward, it is just usually the algebra you need to get there that makes it a pain. So what I do is I take exactly what I'm learning and get the general idea for each section of every chapter. I write out the basic fundamentals of the problems so I have an idea of what to do, then you know it is just a matter of using your algebra to get to that part of the problem.
Everyone bombs classes every once in a while, it's just how college goes. In my opinion, everyone can do all classes, it is just a matter of teaching yourself the correct way. Think about what you could have done differently and the next semester take that approach. You're obviously doing something wrong if you got that grade, especially if you know you're a smart person(which you should). Fix that, you'll ace it the next time around.
If I were you, I'd consider taking precalc over the summer, just to kind of brush up. Precalc is strictly algebra rules and trig rules. It'll seem tedious but when you hit calc again in the summer, everything will be extremely clear and the only thing you'll have to do is focus on bringing down that exponent and subtracting it
Above all, never limit yourself with your mind. Saying something is too hard is loser talk, nothing is too hard, tell yourself you can do it, brush off bad experiences and you'll do better your next time around. Anything to do with math is very rewarding, and the higher you go the more you impress the ladies (meh no wonder i don't get enough women). Anyways, I just wrote a novel, stupid adderal, can't wait til exams are done.