How many references should I use?

Unless you have been specifically told by your marker, or it is noted in the assignment requirements, that you require a certain number of references, there is no exact answer to this question.

The number of references will be determined by the nature of the assignment, what you have written and the sources you have consulted.  If you are worried you have not used enough sources, and therefore do not have enough references, we would suggest you seek guidance from whoever is marking your assignment.