If you applied the sensor the same day you activated it, I recommend being a bit sceptical about the readings. Many of us find the reaction of our body to the alien object inserted in our arm will result in dodgy numbers until the body is used to it it. Therefore, it is common to apply the sensor a few days before activating.
Once the sensor has “bedded in”, I still find readings in double figures or below 4, tend to be less accurate.
As for the daunting needle, it is only used to insert the incredibly thin filament and does not remain.