hcg slow rise

Alysa
On 6/4 it was 20,441
On 6/6 it was 21,649
Had a transvaginal scan on 6/5 measuring 6w1d but based on lmp I was 8w4d (however I have a 33 day cycle so idk if that can change things) 
Dr is telling me bc it didn't double that I will miscarry or can have a d&c but I've read that when the numbers are higher like that they are less reliable/relevant and don't always double like when the numbers are lower...anyone experienced this before? What was the outcome?