Well, try to aim for a C. That's the minimum grade for prereqs at many vet schools. Look for more practice problems and seek out help from the professor and your peers if things aren't clear to you. That's all you can do to improve your grade.
As for being screwed in other harder classes if you don't ace a math course, well it depends. Why are you not doing well in this class? Are you not interested in the material? Are you not studying enough? Do you not understand things? Hopefully you're not a math major, right?
Overall, I would say a person's performance in pre-calc is not predictive of his/her abilities to cope with chemistry, physics, biology, etc. Most science courses have some underlying math involved but at the undergraduate level, it's not typically advanced math (i.e. you probably won't be using things you learn in pre-calc or calculus in these courses). So, if your problems don't stem from poor study habits or an inability to follow directions on a test, you'll probably be okay.
Have you taken any biology yet?
