Same goes for anyone, including you. If you want to become successful at anything you need to work hard on it and improve and see where it takes you rather than setting out an overly defined goal that will stress and disappoint you.
No problem. C- is still not bad, even though I was a straight As student, I will tell you right now that the pressure that comes with it is not worth it. Not only that, they claim to give bursaries to students who graduate with a certain average. I graduated with an average of 96% and wasn't even eligible. So yeah, in my opinion, anything above 50 is worth being proud of.
The only time I would say it's important to get straight As or really close to that would be if you want to be a Doctor or Engineer and are trying to get into one of those competitive entry programs.
Here's the link to one of the books (it's one of the cheapest pre-calculus books out there, this is my most popular one because it's my entire book series collection all in one book):