Empty sac?

keno

I went for an early scan last week and was told there’s a sac but it’s empty… I should’ve been about 6 weeks according to my LMP. Yesterday I saw my obstetrician and he took this image but his machine is a bit dated. I have a follow up tomorrow for another scan at an ultrasound place…what do you all think? Hcg is going up but not doubling, last it was 15000…