Waiting for miscarriage

Hi there. I had an early scan 2 days ago and baby was measuring 6w2d but my dates would be 7w3d. Heartbeat was at 78bpm which is low. I need to go back in a few days to check whether heart rate has picked up or stopped (which is most likely given measuring small). I haven’t had any bleeding or cramping but I feel like now I’m just waiting for the inevitable to happen and I keep questioning ever twinge. Has anyone else experienced this? How long does it normally take for the miscarriage to come?

Thanks in advance