What should i follow?

When I had my first check up my doctor ask me when was your last mens.period so I answered oct 15,later I know na hindi na ako dinatnan ng month of october last was september...so sabi niya if october my edd would be last week of july or first week of august... going to a sonographer she ask me also when last period i told her the same month so sabi niya 6 weeks pregnant ako and the same edd... pero di ko na binago na september lang pala last period ko ... ask ko lang kailangan ko ba sabihin o i correct yung naaabi kong october so i can have an exact month or as is nlng? Salamat po sa sasagot. Kasi kpag september nilagay ko dito sa last period sa app na ito my edd would be june kapag nag follow ako sa doctor na sinabihan ko october edd is july-august. Meju may doubt lang konti hehe. Thank you anyway