I had a bunch of scans with DS#3 for a SCH and by 16 weeks his boy bits were unmistakable. Seriously. To me most u/s images just look like blurry blobs but when my tech showed me a potty shot at 16 weeks she didn't have to tell me what that was, lol. So, my point being, although nothing in life is a guarantee, I can't see how an experienced tech would miss boy bits at 17 weeks. You've got a girl in there! :)