Help please

Sara
So I got my blood work back . My hcg is rising but not doubling after getting my blood work back . I think the initial number was 1600 and went up to 2800 . My progesterone is high . The nurse wants me to come in for another scan on Thursday . 
The thing that worries me is will this be a long enough time for them to see the baby ? 
My previous scan was on Friday October 2 . They saw the gestational sack measuring about 5-5.5 weeks. If I go back only 6 days later will they be able to see a change  or a heartbeat ????
I'm so torn about whether I should go Thursday or postpone in for a little longer ?