HGC rising but not doubling

Momma of 4
My HGC levels were 45 at 3 weeks 6 days, and 4 days later it was 168, doubling every 48 hours would have been in the 180s. Not a huge discrepancy, but also I'm in the lower end of the range even though it's technically normal range. This will (hopefully) be my 4th baby and I've never had an issue with low end hgc, but then again my dr pointed out that we tested earlier this time than my previous pregnancies. Did anyone else have slow to rise levels and still be okay?