I wouldn't worry about it until you get the combined result. They have to look at both the blood tests and the nuchal fold thickness together to come up with a reasonably accurate risk factor for a problem with the baby. Even then, the tests aren't that accurate, and most of the babies identified as being at risk will be healthy anyway.

Remember that the nuchal fold thickness of any baby will change day by day anyway. I would trust in what the sonographer said, until you know any more details.