Gestation changed, size not so much. also premature baby info!?

Went in for a "second opinion ultrasound" today after the first one they said there was no heart tones detected, my doc wanted me to get a d/c right away but I couldn't so I waited a week n a half n went in to another place to get an ultrasound, she couldn't see a heart beat but the gestation changed, the first u/s the gestation was 9 weeks 3 days but this time it was 10 weeks 3 days. And also the size the first time was 2.6 cm and this time it was 2.76 (not much of a change) but I don't understand why the gestation changed, I thought the gestation was determined by the size but the sizes were not off by much. Is there a possibility its still too soon to find the heart beat on an abdominal ultrasound? Also is there a chance that maybe the baby is premature so its not growing as much? I just don't understand y the gestation was differemt then the first time. Its really hartd to accept the fact that I'm possibily misscarring with absolutely no signs or symptoms in almost 2 weeks! Some additional information would be that the ultrasound technician said that there was no halo over the babys head and she said most of the time especially when its been over a week later she said a halo usually forms over the babys head but mine didn't have one. I'm so confused here, I'm so scared to get a d/c with fear the baby is still alive in there. Some one please please provide me with some information here, especially about the gestation change and size and also some info on premature babys and how they grow and show up on ultrasounds. Thank u so very much!