My wife has Diabetes and recently switched to a CGM. She also saw the insanely inaccurate results.... BUT it improves. After a few hours the numbers get more accurate as it adapts to you. Now she does a thing where she overlaps the old sensor with the new sensor for a couple of hours every couple of weeks. She also still occasionally uses the finger prick method because its results are more indicative of where you are going in the short term.