Congrats on your pregnancy I remember your story and the elation at the arrival of your girls!
I don't have a similar story but with both my successful pregnancies had lower numbers than you at the start and was always given the hushed let's see what happens response from ob.
So I say everybody is different and the rule seems to be doubling every 48 hours but when you look into some research they say doubling every 72 hours is a good gauge.
Stay positive and wait for your next blood test. I'm crossing everything for you x