IVF Beta Levels Not Doubling

Amber
I am recently pregnant. I had my first beta levels at 56 and 48 hours later I had them at 90, which is only a 61% rise. My doctor said that it meet standards as it should be at 60%. But I am worried because it didn't double and it is supposed to double every 48 hours. I am so nervous. Anyone have any advice or hope that you can offer??? I am feeling so sad about it. Thanks