Welcome to HCM.
Since the baby appears healthy, i think there is nothing to worry.
Mistakes and misinterpretation in sonography
, do occur, even with experienced sonologists.
In Down's syndrome the development milestones in the child are markedly delayed, the child tends to put out the tongue frequently.
From what you have said I think the child is perfectly healthy and does not require any further investigations or treatment.
You may thank the Almighty for delivering to you such a healthy child after initial scare.
Wishing the New Born, BEST OF EVERYTHING IN LIFE.