That's normal. I was high risk with daughter and had scans every week from 6 weeks to 13 weeks and then every 2 weeks and then every 3/4 weeks and I don't think I ever measured spot on, even when going every week. Baby would be a day or so behind or ahead. On my OB's ultrasound machine, out by where the date comes up when they measure baby, there is a +-6 days, meaning the date can be out by that much and it's normal. I wouldn't worry, especially since you had a good heartbeat! Good luck with your MaterniT21 results. I had the test done back in 2012 bc of my age and was a nervous wreck waiting on results. All was good tho and I hope it is for you too.