Nuchal translucency scan

I am 9 weeks 5 days and I just had my first ultrasound 2 days ago. My doctor told me my babies heart beat and length were good, but that there was a thickining in the back of neck. She then told me that this could mean that my baby has Down's syndrome! However, she said that its so early that I More than likely have nothing to worry about, but made me an appointment with the high risk center for an ultrasound at my 13th week. I am not sure what to think! Should I be worried? Is this really that normal to see at 9 weeks? I  ill love my baby no matter what, but I just want him or her to be healthy. I have been a mess ever since, and was just wanting some opinions. Thanks so much!!