No of course it isn't bad, C is still a pass. Believe in yourself, the worst thing you can do is go into an exam telling yourself you will fail. You've worked hard, you've revised, you're put in your best effort and at the end of the day only you know how hard you tried. You are not defined by a number or a letter on a piece of paper, C's get you into college and that's all that really matters at GCSE. Good luck, I know you can do this.