Your oxygen level at rest should be between 92-95 depending upon the stage of the COPD. too much oxygen like above 95 % decreases brainstem stimulation to get rid of CO2 which gets accumulated in COPD.
Blood oxygen should not go too high and it should also not go too low like less than 90.
If with exertion like on walking your oxygen drops belwo 88% you become elegible to get supplemental oxygen.
oxygen saturation with finger tip monitors may not be reliable in certain cases.
Please follow up closley with your doctor.