Hcg slowing down

I’m really concerned, I won’t have my first ultrasound until Monday afternoon to check for viability but my hcg numbers have me so worried.

11dpo- 17

13dpo- 40

19dpo- 476

26dpo- around 6500 (don’t have exact number)

As you can see they were doubling as they were supposed to at first but this last draw didn’t. It should have been somewhere above 7,000. I’m so worried and Monday feels so far away. I am estimated to be almost 6 weeks. Anyone else experience this?