As I went through college (and I think everyone more or less goes through this) I learned to care less about marks as a whole and more about what I learned in that class/if there the knowledge is easily obtainable elsewhere. However, I'm fortunate enough to be in a field that doesn't explicitly require grad school (compared to say, those aspiring to be doctors) and that internship experience/generally more concrete interviews generally lessen the requirement for having really high marks.