Libre sensor

It is common in some people. All mine with one exception have read lower than my finger pricks, but not by any more than 1mmol/l and often less.

Did you wait 24 to 48 hours between attaching it and activating it? This gives your arm time to adjust to the foreign body inserted in it.
Do you finger prick then wait around 15 minutes before you scan? (There is a time lag and this varies from person to person)

Once you have some sort of average discrepancy it will make more sense, and as you are a diet only T2 (like I am) all you are looking for are trends, rises at times you weren't expecting, and what happens overnight when you are asleep.

As @Bluetit1802 mentioned, two things to consider are
- 15 minute delay compared to finger pricks
- 24 to 48 hours for your body to get used to having a foreign body inserted. This affects bg reading.

The Libre is factory calibrated. We are not all the same as a "factory body" so some of us experience more discrepancies. I have found third party apps such as Glimp which allow you to calibrate the Libre against finger prick is more accurate.

However, the value of the Libre is not the absolute value, it is understanding the trends. I compare using Libre to replace finger prick with having a smart phone just to make phone calls.