Non viable twin ?

I went for my first ultrasound today the first baby looks great measuring right on time. The 2nd sac looks the same size and has a yolk sack as well as a fetus that is hard to measure and hard to see heartbeat. The dr said she doesn't think it is a viable pregnancy but it could still progress. I am 6 weeks 5 days. The way the babies a presenting I am trying to stay posative and say it's hard to measure the 2nd baby because the big baby is right on top. This is a bad picture. The bottom sac is bigger and has yolk sac. Has this happened to any other Momma's out there !