I'm not sure what the doctor was talking about saying that normal blood glucose was 300 per dL.
"For someone without diabetes, a fasting blood sugar on awakening should be under 100 mg/dl. Before-meal normal sugars are 70–99 mg/dl. “Postprandial” sugars taken two hours after meals should be less than 140 mg/dl"
Anyone I've ever known with a blood sugar level of 300 needed to be put on insulin to bring it down... If that's what your blood sugar reading was, you should talk to your doctor and have further tests because that's too high...