Missed miscarriage ?

Had a early scan I thought I was ment to be 9 weeks but the “baby” was only 6 weeks with no heart beat, they are booking me in for a rescan but if I had a missed miscarriage at 6 weeks and it still hasn’t come out how long dose it usually take? It was 1st feb the scan so by then I’d of miscarried 3 weeks before so that’s now a month later ? Xxx