When is my due date

Typically I have 28 day cycles. I just got a positive two days ago. This last cycle I didn’t get a positive opk for three weeks. I’m trying to figure out when I would be due...

Date of last period is sept 28, that would put me at 4 weeks, 4 days with a due date of July 4.

Got a positive opk on Oct 18 which puts me at 3 weeks 3 days and a due date of July 10-12.

Do I go based on my ovulation date or date of last period? I feel like if I’m only 3 weeks along it would be too early to get positive tests