Sorry to hear that you had such a horrible experience,
snowden19. And welcome to GMAT Club!
This might sound totally counterintuitive, but I'm 100% convinced that everybody needs balance in their lives in order to perform well on this test. The GMAT isn't a knowledge-based test. Sure, you need to have a grasp of fundamental mathematics and grammar and reading, but it's ultimately about precision and focus and logic and reasoning. And that takes more than just hours and hours of brute-force studying. If you're not 100% sharp and clear-headed on test day, you'll underperform your skills.
And it sounds like that's at least part of what happened in your case. I don't know what your practice test scores were, but if they were consistently higher than they were on your actual exam, then you presumably made mistakes that you don't normally make.
Everybody is different in terms of their appetite for studying, but we usually discourage our students from studying for more than four hours in any one day. Most people will start making careless errors -- misreads, silly calculation mistakes, that sort of thing -- once they start getting fatigued in, say, hour #5 on any particular day. And on an adaptive test, that's the kiss of death. If you make silly errors on questions that are easy for you, you'll just see more easy questions, and your score can plummet in a big hurry. So don't overdo the studying! Quality ≠ quantity.
And sleep, diet, exercise, and a little bit of joy in your life also make a big difference. Yeah, this test is hard, and you might need to work really hard to beat it. But you can't just bludgeon it into the ground with the brute force of hundreds of hours of studying. So say hello to your friends again, and make sure that you keep some balance in your life. You can't memorize your way to an amazing GMAT score, but a clear, well-rested mind will definitely help.
And poke around this section of the forum for inspiring stories. You're definitely not alone in your struggles!
Keep us posted, we're rooting for you!