Glucose screening in 3rd Trimester

So, I’m 30 weeks pregnant, and my doctor just ordered my glucose screening last week. I spoke with another doctor and she said I should have had it in my 2nd trimester, mostly because your body changes way too much in the 3rd to get an accurate result. Did anyone else have a glucose screening in their 3rd? I was told it’s almost impossible to pass a screening in the 3rd. I failed my screening by 1 point so she’s sending me in for a 3 hour. It has stressed me out for the past week. Any advice? 😞