OH MY GOD......I got My BFP !!?

Yesterday i took pregnancy test and i got positive..... i am so happy, And today i went to doctor for blood test. and she took an ultrasound scaning, in that we can found the sac , she said it's too early to find anything else. I would like to know that is this ultrasound scanning is harmful in the fourth week of pregnancy??. And is that sac means i am pregnant??