IN NEED OF ADVICE PLEASE!!!!

So I found out I was expecting with a hpt 11/12 yay I'm pregnant!!! I went to my first doctors appointment on Tuesday and had an early ultrasound done, found out I was 8 weeks and expecting twins yay again!!!! During the ultrasound I was told that baby B is a week behind baby A. She wasn't concerned about that the concern came from baby B's sac, which is measuring 2 weeks behind. I have another appointment coming up next Friday to see if baby B is still viable. I guess my question is has anyone had this experience and had an positive outcome?? Thank you!!!