Anyone? Yolk sac?

So I went to the ER concerning my spotting and mild cramp. I had blood work and ultrasound done. According to app I'm 7w 4d but the ultrasound read the baby at 6w 3d. Also the doctor said there was a visible GS and cord? Or something like that, but there was no yolk sac or heartbeat detected. They also said my HcG level was at 1100 and they said that was low. They diagnosed me with threatened miscarriage. I have to call my OB on Monday to get a repeat of blood work and see if my numbers have doubled. I'm just hoping I'm early in pregnancy or implanted late, I have irregular periods. I'm just wondering, has anyone had a similar problem and had good outcomes to it? Thanks ladies.