Reassurance needed

Hi all, 
I am 6 weeks pregnant and have been for a scan today at the epau after some spotting measured at 6 weeks 1 day and had a heartbeat, but was 'lying low in the cavity'. We were told this could mean a possible miscarriage. Has anyone experienced this, or does anyone have any advice? 
Got another scan booked in a week but so scared we are going to loose this baby! Been ttc for 3 years and really hope this one sticks!