I have a question!

Brittany 💕 • Hi I'm Brittany I'm 20 I had my first baby at 18 she's a heathy 1 year old now I am pregnant with baby #2 I am engaged❤️
So this is my 2nd baby I had an ultrasound today the baby will be 8 weeks tomorrow but the sac is mesuring 7 weeks & 2 days is that normal ? Or ok my first baby had an awesome pregnancy with her she's 1 now  should I be worried ? The babies heart rate was 178 good strong heartbeat