There are two kinds of screw-ups: those you cause, and those that couldn’t be avoided.
When you mess up, you are going to feel badly about it but then you will have to get past it. Sometimes you get past it a little more easily because the offended party might help ease your pain a little. Other times, it might be justifiably all on you. You screwed up; now you own it.
Personally, I find this easier said than done. I can forgive anyone easily but not myself. I have almost a lifetime of pointless Catholic guilt that I have to deprogram from my operating system. Life will be so much better when we are all apps.
Accept that things went wrong, horribly wrong, and you feel badly. But understand that how you feel doesn’t change anything for anyone, not you or the people affected. Nobody cares how badly you feel about it, and that is completely understandable. So moping around and punishing yourself is pointless; you are literally killing yourself and no one is benefiting. I will remind you that for one notable exception, nobody likes a martyr.
Forgive yourself; it’s the compassionate thing to do.
There are some great lessons that come from humility. You will revisit the circumstances of the screw up and make the appropriate adjustments. You will establish or perhaps re-establish some rules that will help you avoid similar mistakes in the future so that others may benefit from this. You may determine that you have too many things going on, or not enough, or that you are implementing the wrong strategy. That could save you all kinds of time and money, not to mention mental health, in the future.
You will likely learn a little bit about yourself along the way too.
I’m sorry it all went wrong for you. I’m sorry if someone else caused it too. Now get on with it.