I would suggest warming up much more gradually. Start with 20 minutes at well below your expected aerobic threshold pace / heart rate (e.g., 9km/hr, 120bpm), and see if that gets you a lactate reading below 1.5mmol/L. If not, try again the next day even slower.
Also, make sure to use an alcohol swab to clean your finger, and wipe off the first drop of blood. Otherwise, you may end up with sweat contaminating the blood sample and giving bad results.