Not all of your marks can be top grades. C is OK - not great, but not terrible either. One of the skills you're developing is the ability to stay motivated through disappointment. As you're disappointed with a C, make sure that you understand how you lost marks, and correct those points in your next coursework to aim for a better mark.
TBH you're probably expected to include references and appendices (if you need to) anyway. It's whether the references have been done correctly and whether the appendices were necessary, which might prevent you getting marks deducted. If your feedback doesn't tell you what you need to improve, go and ask the person who set the assignment.