HCG Levels not doubling

Emily

Hey, so I'm 5 weeks and 4 days along and had my labs done.

Monday:1523

Wednesday:1721

My level only went up by 198 in 48 hrs. I'm so scared it'll be a miscarriage. Dr said not to worry yet and we'll do another blood test on Monday. Anyone else have anything like this? I just don't know what to think.