Measuring 5 weeks supposed to be 6

Hello. So ive had 2 previous miscarriages. I found out the 19th of feb i was pregnant again. Im supposed to be 6 weeks already but i only measured 5 weeks at my ultrasound today. I couldnt really tell if there was anything inside. All i could see was a gestational sac... wondering if this had happened to anyone else? And if it ened with a healthy baby? Im a little emotional right now. Just because of my past 2 miscarriages. But tryingbto remain hopeful.