Due date confusion - scan results coincide with negative ovulation tests

I had my 12 week scan yesterday on what I believed would have been 12+3 according to the first day of my last period (15th August) and regular 28 day cycle.

However the sonographer did the measurements and baby is 13+1. I appreciate that the scan is more reliable for dating, what confuses me is that the days that the scan suggests was conception date (cycle day 10) I had negative ovulation tests. I have done ovulation testing daily for months and was fortunate to get obvious positive tests around day 13 of my cycles.

So is it the original 12+3 due to he negative ovulation tests or 13+1 according to the scan?

Super confused??