Yeah, I had 8 months of pristine white where that second line should be until one month..... two lines.
Congrats mama! Wondfo's are pretty accurate. Do you chart or do you have any idea when you had el sexo? This would be useful. If you are SURE you didn't have sex during ov dates (or right before, as those sperm can hang out for like 3/4 days, lurking that egg) then you may want to just make sure to tell your doc that you'd like to use u/s dating or even your best guess at conception rather than your last menstrual period (LMP). If you use your LMP and you actually ovulated way late, it can throw things off, make you freak out if they say baby is measuring too small (when really that baby got made a week later than they're expecting) or at the very end, they may want to induce if you're only 40 weeks or something. So the due date is not super duper critical but it can have some meaning behind it.
That said, I think the dating u/s early on can be really accurate (unlike the size u/s later on!)
Again, congrats!
PS. I ovulate much later than I thought, too. First baby I was ovulating like day 14 constantly - this baby was more like day 18.