initials only

Hi all I need some help,

I am trying to update a paper to AMA style. The references are all correct in my library but they keep showing up with just initials in my paper. 

For example: 

JC B, VJ S, EA M, et al. Sentinel lymph node surgery after neoadjuvant chemotherapy in patients with node-positive breast cancer: the ACOSOG Z1071 (Alliance) clinical trial. JAMA. 2013;310(14). doi: 10.1001/jama.2013.278932.

Why arent the last names included? I have tried editing the style but maybe im doing it wrong. Thanks