Coordinates are not quite right

I'm in a world that I created 3 days ago, I tried to make a symmetrical build but for some reason I couldn't center it the cords are x:-756 – x:-782 I want it to have double doors so therefore the 'middle' is -769 and -770 right? No, for whatever reason I only have 'one middle' at -769. I am 100% sure I am reading my coordinates right