Do I need to provide only the number of references requested?

No, you can provide the details for as many references as you wish. This can be beneficial because one referee might come back quicker than another. 

If you would like to enter an alternate referee, or if you realise you have provided the wrong email, go back to the link in the original email and add another referee. You can do this by clicking the “add another” button at the bottom of the page