If they got a heartbeat that means it was closer to 6 weeks than 5 - the heart starts beating at about 5w4d.
A few days is neither here nor there, early pregnancy scans have a margin of error of +/- 7 days.
A heartbeat is a very, very good sign...hang in there I'm sure everything is as it should be. Early pregnancy is such a head game if you've had miscarriages before or fertility treatment