7 weeks baby measuring small 😕 terrified of miscarriage

Ja
I am 7 weeks 6 days pregnant after trying for 13 months. This is my first pregnancy and we used clomid and a trigger shot and were so excited to find out it finally worked! 
Yesterday at my second unltrasound at the RE we saw he baby's heart beat (100bpm) but the RE said the baby was measuring small. She didn't say how small but I think I saw 6 weeks 3 days on the screen. I know my dates can't be wrong because of the trigger shot and all the monitoring by the RE. Plus we had an ultrasound 11 days ago that showed the sac and the RE said the baby didn't grow as much as she would have expected since my last ultrasound. 
We are going back in a week for another ultrasound but I'm terrified. I feel like this baby is going to be taken away from me and I'm already crushed. Anyone have a similar experience and it not end in miscarriage? Help!