Measuring earlier but I know when I ovulated

My LMP was February 15th, I ovulated on March 2nd or 3rd (used OPKs), and should have been right around 7 weeks yesterday. But my ultrasound yesterday measured at 6w1d. And there’s so much space around the baby, is that normal? Other early US that I’ve seen don’t look like that.

The heartbeat was 126 and very strong... should I take that as a sign that baby is ok for now? I’ve been spotting for over a week, I’m afraid that baby isn’t growing fast enough.

Thank you for any feedback