Your belief about the normal range of blood glucose is incorrect. Your doctor is right to be concerned because you meet at least one of the diagnostic criteria for being what is considered pre-diabetic/ metabolic syndrome.
From the American Journal of Medicine ( June 2008 (Vol. 121, Issue 6, Pages 519-524):
“Subjects developed diabetes at a rate of less than 1% per year during a mean follow-up of 81.0 months. Each milligram per deciliter of fasting plasma glucose increased diabetes risk by 6% (hazard ratio [HR] 1.06, 95% confidence interval [CI], 1.05-1.07, P < .0001) after controlling for other risk factors. Compared with those with fasting plasma glucose levels less than 85 mg/dL, subjects with glucose levels of 95 to 99 mg/dL were 2.33 times more likely to develop diabetes (HR 2.33; 95% CI, 1.95-2.79; P < .0001). Subjects in the 90 to 94 mg/dL group were 49% more likely to progress to diabetes (HR 1.49; 95% CI, 1.23-1.79; P <.0001). All other risk factors except sex were significantly associated with a diabetes diagnosis.”
Basically, every full milligram above 85 you are (so 86, 87, 88…) increases your risk by 6%.
Unless you know the false-positive rate of the test, as well as Type I and Type II errors, it’s somewhat naive to demand an additional test. If there is a high rate of false positives, or if the OP were truly borderline higher risk (starting around 90 to most practitioners), then that would be another question. In this case, the OP is so obviously at an elevated risk, it would be a waste of resources to do another test.