First ultrasound worries!!

I went to my doctor the other day for my first ultrasound. It was transvaginal and my doctor seen the gestational sac in my uterus but thats all they could see. They scheduled me for a second ultrasound next week. Has this happened to anyone else? Should i be worried that the baby couldnt be seen or heard yet? They thought i was 6 weeks but after the ultrasound my doc said i must not be that far yet. I had a miscarriage earlier this yr so im worrying bad this time.