Blighted ovum?

My husband and I went in yesterday for our first ultrasound. We were overjoyed and couldn't wait to "meet" our first child. The u/s tech could only find two empty sacs :( (twins). The Dr. prepared us for a miscarriage. We go in next week for another u/s to confirm. I thought I was 9 weeks 2 days based on the first day of my last period but the sacs were measuring 6 weeks 4 days and 5 weeks 2 days. Is there hope or should I prepare myself for a miscarriage?