confused

So i had my first ultrasound and prenatal visit today. They told me baby measuring only at 6 weeks and 2 days and they not sure if its a viable pregnancy. I should be 8 weeks and 4 days from my lmp. I am worried not sure if i am going to miscarry or maybe it is too early. They also did not hear the heart beat also so idk what to think. Has this ever happened to any of you? Midwife will call tomorrow with beta results to make sure levels are going up. Levels on sat when at er were 44,000. Advise plz