Informal ultrasound?

Ok. I was hoping someone has had a similar experience since I am freaking myself out worrying. I went for my 8 week first ob appointment and my ob wheeled in a Doppler/low resolution ultrasound machine. So it wasn't a real ultrasound. Pretty much she just looked to make sure it was in the right place and that there was a heartbeat. We saw the heartbeat flicker and heard it and saw our little bean but she said I was either measuring a week behind or that it was nestled up in there and couldn't get a good measure. She wants me to come back in 5 weeks for my first dating ultrasound. I can't stop thinking about it and worrying that baby isn't growing like it should. But maybe it was just the crappy machine. Someone please help ease my mind and tell me this has happened to someone else. Thank you mommies!! ?