OK, so it was just a quick scan of an in-office ultrasound machine by your OB? In that case, I would request a biophysical profile before going anywhere further with this. Your OB may have some basic training in using the ultrasound machine, but none like an ultrasound tech. It's important to look at all the factors of a biophysical profile: the movements of the baby, the levels of amniotic fluid, the reactivity of baby's heart rate, baby's breathing movements, and placental grading. The grading will tell you whether or not, along with other factors of the profile, whether or not your baby needs to be born early.
What if you had not had that scan? Would your OB think something was amiss? A placenta that is not functioning results in poor baby growth, a heartrate with little or no reactivity (baby does not move much and when he/she does, the heart rate goes up just a bit and then comes right back down, whereas in a healthy baby, the baby moves alot and the heart rate increases with movement and stays up about 10-15 beats a minute for a period of time...). So, if your placenta was really comprimising the health of your baby, your OB would have noticed this in other ways. YOU would have noticed it, too, with decreased movements.
If you're wanting to confirm the health of your baby, then a biophysical profile might be a good next step. It surely would make sense and your OB would probably be supportive. The BPP grades various factors and the most common "problem" seen is low amniotic fluid, which in late pregnancy isn't always an issue. I would suggest drinking alot of water (2-3 quarts a day) over the few days before the test if you do it.
Anyway, be firm in the confirmation of your dates. You know when you conceived and your charting should take presidence over anything else.
If you need more information on the BPP or have any other questions, let me know. BTW, you are pretty lucky to be there in Italy! We went last year and growing up my dad was in the Navy, so we were always trying to get stationed in Naples. Heh! Instead, though, we got Cuba. ack!