Is it a new sensor? I ask because you may be experiencing "insertion trauma". It is common for our body to react to the alien object in our arm when it is first inserted which will affect the readings. This is why some of us will insert a new sensor a day or two before activating it.
Could you be dehydrated? Lack of fluid can affect the readings from a CGM.
Have you checked your finger prick meter against calibration fluid recently. We use our meters so often that we come to rely on them and forget that a finger prick meter may be out - they only have to be within 15% accuracy. If your "true" BG was 6.4, it could be reported as anywhere between 5.4 and 7.4. With this in mind, Libre may not be that far out.