Aside from any marksmanship or wind estimation errors, you're missing because you're introducing errors from completely unnecessary arithmetic.
I will admit that the one time I went to the 500 yard range, I probably shouldn’t have. I wasn’t ready for that. I don’t know my ammo and how my rifle shoots it well enough to have accurate drop info for that distance. I put the ammo data into the Hornady ballistics app and used the adjustments it gave me. However, I know that’s not 100% accurate. I haven’t shot paper any further than 200 yards with anything but cheap Winchester white box 6.5cm.