Just made a massive mistake at work and freaking out a little

I've recently been promoted and given a very large project to manage. It's been so busy and stressful and I've felt out of my depth the whole time.

I've raised this with the project lead a few times but been told that I'm doing great and have been handling things well, but this mistake throws that all out the window.

But I've just realised I've made a massive mistake and we're only a few days out from the deadline. I've been working such long hours and I'm so exhausted, but I've completely overlooked a crucial part of the project.

This project has meant a lot more management and meetings and has taken me away from the actual doing of the job, which is why I didn't spot this sooner. I've also been trying to rebalance my life and spend less time at work, but I'm feeling like that was a mistake and now I've landed myself in the shit.

I'm spiralling a little bit, I feel like I don't deserve my promotion and that I'm never going to get to the position I want to in my career.