1 c in an honors class, with the rest being all advanced they won't kill you for it.
Are you on semesters? If so than you are probably coming up to your final...Hire a tutor. As long as you know you gave 100% and couldn't give anymore you'll be fine..
Remember it is the whole candidate, make sure you are taking the best course load that you can handle,(SAT/ACT is also a part of the equation) participate in EC's and do well in the CFA.
My DS received a C in Trig, (10th grade) at the Sen interview they asked him pt. blank about it..he answered honestly and said just didn't get it. I think the grade jumped out at them because he was in an advance Math ( Al I, GEO AND AL II were all A/B+) early and then he took discrete and statistics after that and pull A's. He is in Calc now. Thus, his transcript looked a little wacky, but they will excuse a bleep on the screen, lots of bleeps is a different story