csab, please don't stress about this too much. I know it is easier said than done.
These scans can be terribly innacurate at times.

I was told my DS (now 8 years old) had one leg longer than the other and he would probably walk with a limp. He was born totally normal with two beautiful legs the same length.
I was also told my last DS was going to be a BIG baby and that he was "above average", he was my smallest baby, born at a lovely 7 pounds 3 ounces.

You and baby will be fine, you have an enormous amount of good vibes coming your way...we are all thinking of you.