
If the test was correct then the earliest the ova could have been fertilised was at the second mating,a dn possibly not for another 3 - 3 days. then allowing for the test being off by a day or two, might mean you had mated too early.
Had she gone off/become less willing after the second mating.
it would have been better not to have mated her until the second mating for the first mating and tried again two days later if travelling for each mating.
I have just had a litter from my girl who was not tested. She was amted alternate days over five days. She was two days late to first mating, so she probably didn't take until after the second mating at the earliest, but more likely the last.
Generally I have had maiden bitches whelp between 2 - 5 days before due date for first mating, ans it is rare for them to go the full time.
The one I had blood tested at a lab was mated the day after ovualtion and the next two days and whelped two days early.
So it could be that she took up to 6 days later than the indicated ovulation day.
Fingers crossed for the second scan.