Hcg not quite doubling

Good afternoon ladies

I an currently 6w5d pregnant and I've had a couple hcg levels drawn and the first 2 were 48 hours apart and had doubled. Then I had my 3rd draw 8 days later and it should have been approximately over 6000 but mine was 5730. Is this still OK? My Dr is having me do an ultrasound in 2 days to check placement since the numbers are exactly doubled. Anyone else have this happen and everything be ok??? I'm really worried. I've already had 2 miscarriages in the past 2 years

TIA!!