Thank you for your query at DoctorSpring.com
Prolonged exposure to high VOC stains and paints is what is associated with probable birth defects in the unborn child.
In your case, the exposure was very brief, and that too with the windows open.
Also, once it has dried and aired out, there is no reason to worry.
All said, in my estimate, you should not be worrying at all.
The exposure has been negligible.
Also, at 8 weeks, please get an ultrasound scan done to confirm the well being of the baby.
All the best
Please feel free to discuss further.