Pray for positive outcome!

I went to the doc Tuesday thinking I was 6w4d for an ultrasound they did a transvaginal one and saw the baby measuring at 6w1d but couldn't fine fetal heartbeat but my doc said not to be worried he said it could be early dates off or the machine isn't as new as some others he us having me come back next week to check on growth and heartbeat...has any one had a positive out come in similar situation? I'm a nervous reck! This is my 4th baby and u have never had any problems before so I'm freaking out!