I'm terrified.

Andrea • 31. 🦄 Mommy to 2 boys, stepmommy to 1 girl & 1 boy. Expecting baby girl in March!
I had an ultrasound today. By my dates, I figured I was 6+5 but my gestational sac is only measuring 4+2, and you can see where baby should be, but there's no heartbeat or anything. My nurse practitioner said I have a 50-50 chance of either being early or of miscarriage. I'm having levels drawn today and then again on Monday, and a second ultrasound on Wednesday. 
Im terrified and I can't stop crying.