The first Ultrasound... not sure what to think

I need some encouraging words ladies.... so I want to start of by saying I do not know exactly when I conceived due to irregular periods. My last period was 10/31 and I did not have one in November. My husband and I did the baby dance the week of 12/7 (not sure the exact date). I had a negative test 12/11 and a faint positive on 12/24. My HCG levels were fine but when I got my ultrasound today the baby was just measuring at 6weeks 2 days. No heart beat yet but the doctor says it could be too early so I go back next week. I am just so nervous that the baby might of stopped growing :( any positive words or stories like mine would be great! Thanks in advance!