Update on hcg low numbers

On Wednesday my hCG was 800 and today it’s 1200. Unfortunately, it was a four day break due to the holiday. I should be seven weeks two days today. I know when my last period was and I know when I got my first positive ovulation test. Is there a margin of error that could occur? Even though I tracked my ovulation and my first positive test was on November 27, could my body not have ovulated till way later and I’m actually not as far as long as I think? They are glad that my HCG is going up We will repeat the hCG blood draw on Wednesday.

So could it change and I could be not as far along than I think, and is it still possible to have a viable pregnancy and my levels not double?