doctor has me terrified!

Ga
I had my anatomy scan a few days ago, and everything was absolutely perfect. But she did say he was in the 86th percentile weight wise, and that we needed to keep an eye on it and that I would end up having a C-Section because he would probably be around 11 pounds at 40 weeks. I don't have GD, my glucose levels are perfect and I've been eating well/staying active my entire pregnancy thus far. 
I'm just TERRIFIED because I have heard from multiple women that the weight check isn't always accurate, and I don't want to be told, "Alright, your baby is gonna wind up being 10-11lbs, you're going in for a c-section." and find out he is only 7-8 lbs at birth and have gone through a c-section for no reason. Has that happened to anyone? I want to avoid a c-section unless medically necessary and I feel like my doctor just caused me so much unnecessary stress!