Gestational age is dated to your LMP. The fetal age will be 2 weeks less than that. The fetal age starts at conception/ovulation.
Gestational age = fetal age + 14 days
It is normal for the doctors to work with your gestational age. That way you will be around 40 weeks at birth, but your baby will only be 38 weeks old.
Sorry for the confusion. Doctors should really explain this to their patients, but they do not.