I think you need to remove the GeoRange value. Note that GeoRange->d means radius d.
GeoGraphics[GeoCircle[sampleCenter, Quantity[5, "Kilometers"]],
GeoRangePadding -> None, GeoBackground -> "StreetMapNoLabels"]
Or do you want only the interior of the circle?
GeoGraphics[{GeoStyling["StreetMapNoLabels"],
GeoDisk[sampleCenter, Quantity[5, "Kilometers"]]},
GeoBackground -> None]