thank you for asking your question.
Measurements of the fetus can differ according to who does the scan. Ask 10 doctors to scan you and their measurements might differ. But your baby is "allowed" to differ plus/minus 2 weeks - this is then still considered within the norm. What is also important is the development of the size. Early scans are important to define the estimated date of birth. doctors often look at curves of the growth development.
As you can see Baby`s head is 1-2 weeks larger than the norm. Baby`s abdomen (tummy) is norm - same as your pregnancy
week and baby seems to have long legs (are you or your husband tall?) So all together that seems okay.
Having high amounts of amniotic fluid
can 1) be nothing to worry about 2) an indication of diabetes in pregnancy - gestational diabetes
3) sometimes due to infections. 4) Baby can`t swallow the fluid - as the connection between the esophagus
and the stomache is not there - (but then the doctor would have made a note that the stomache wasn`t visible in the scan - )
The first two being the most common. I would suppose that your doctor will do a "sugar test" and measure your glucose
levels after drinking a glucose solution to see if you have gestational diabetes (don`t worry can be well treated and won`t`cause baby harm) and he might check for any infections.
In most cases no reason is found for the high amniotic fluid.
All the best!