I know a couple of people who are at a top 10 school and several others who are at top 20 schools with a C or 2 on their record. I have some friends who will apply next year with a couple of Cs on their record hoping for the same... Anything's possible. A C can be overshadowed by well-roundedness, much better grades later on, strong EC's, etc..... anything's possible, dont give up!