Im really scared someone help

Hey everyone so on Jan 2 2016 I found out thru at home pregnancy that I was pregnant went on Jan 4 2016 to the doctor confirmed I was 6wks based on my last period so today will make me 7 weeks I went to a dating ultrasound today and was told that it was to early to see a baby or heartbeat in the sac. What I never been thru this what is going on?? What does that mean?? Will my baby appear?? Will my pregnancy go full term?? I'm so scared this is my 2nd pregnancy I really want this baby!! I can't stop crying can anyone help me!!