hcg rising but not doubling

I am a 23 year old female who recently had a chemical pregnancy. My OB tested my hcg levels at 6 weeks 2 days, and it was 39,418. Around 53 hours later, we tested my hcg again. It was only 53,045.

I’ve read hcg stops doubling at a certain point - is that what’s happening here, or should i guard my heart?

thank you!