Glucose Tests 😒

So I just found out that I failed my 1 hour glucose test which means I now have to do the 3 hour test. I honestly don't understand how I failed.. I followed all of the instructions. I'm 27w5d today and I've always eaten a healthy diet, I exercise 4 times a week and I've only gained a healthy 9lbs thoughout my entire pregnancy, nor am I overweight or have ever been. My doctor told me I was doing great with my weight, my glucose levels have always been within range every visit. I know that I'll likely pass the 3 hr test but it's a pain having to do it at all. Almost everyone I know and everyone I've been reading about that failed the 1 hr test has passed the 3 hr one, I wonder why that is? 😕