Incomplete miscarriage

I am supposed to be 11 weeks along today but I woke up with brown blood and have had it for the past 2 days no actual bleeding yet but doctors say I’m miscarring and that the baby has no heart beat and quit growing around 6 1/2 weeks and I have done nothing but cry and be depressed I don’t know what I have done wrong or if it ever had a heart beat . It feels like I have a broken heart that can never be healed also doesn’t make any sence that my hcg levels are 24,000 if I lost the baby at 6 1/2 weeks