Terrified

So I had my first OB appointment yesterday to make sure if babies due date, well they did both a pelvic ultrasound and a transvaginal ultrasound as well. They said that baby is not measuring as far as they thought but the Yok looks great...i go back on Friday to take another blood test to make sure my hCg levels are rising. I’m absolutely terrified that there’s a chance that baby isn’t growing...I need something to calm my nerves has anyone else had something like this happen and have good results?