Measuring 5 weeks (no fetal pole) instead of 8 weeks

Ashley
Today was my first ultrasound should have been about 8 weeks based on missed period. Ultrasound found a 5 week sack. I go back in 2 weeks to see if we can see heart beat. Anyone have a similar situation and there be a heart beat at next visit? I'm so worried it'll turn out to not be a vital pregnancy.