Confused!!

Hi everyone, first time to post here, i just have a question though regarding sa edd ko. my edd if im going to base on my period should be on Jan 04/20 however on my sonogram result it shows there na yung edd ko is Jan 16/20 which made me confused yung balik ko kc sa ob is january 03 pa. i just need to know lang po. thank you in advance sa sasagot ?