Please don’t beat yourself up OP, it sounds like you’ve done incredibly well. Focus on the positive.
I think lots of people (including Overeaters like me, Bingers, Bulimics and under-eaters, and other kinds of addicts) can’t ever eat entirely intuitively because our intuition is a bit shit. None of us are good at everything, and for you and me and millions of others intuitive eating is a weak point. I think it’s a lot less painful when you just accept it.
It might be helpful to think that this is a helpful learning experience so next time you are going to a festival or on holiday, you need to think in advance about what you are going to eat and how you will keep an eye on yourself.
As you say, things have to change a bit now because you are living a more flexible life, so you can’t know exactly what calories you will be eating at a Festival - but the deal is, if you want to go, you have to eat regular meals.
So plan next time how you will manage that- one idea night be to take muesli bars and apples for breakfast, and buy a latte. For lunch and dinner there are usually lots of bean stew with rice and salad or pitta type options that are pretty healthy. you take a notebook or use an app on your phone to note that you have eaten 3 meals and a snack if that’s part of your plan. Never mind other people haven’t - you need to.
I wonder if it would be helpful for you to get some counselling to help you manage this new phase of your life? It sounds like you are moving forward really well, but some support might be useful. BEAT is a good place for advice, or the Nightingale Hospt has people on staff or Shahroo Izardi is a behaviour change expert I think is really good. It’s important to have someone with good experience of eating disorders.
I suspect that ‘saving’ calories for a social event is probably not something that will help you, and it throws you back into a weight loss mentality. But if you need a way to manage it, then one idea might be to incorporate some extra snack allowance into your weekly food plan - which you either eat or drink at an event, or just through the week if nothing is going on.
Finally, I think trying to make up 3 days worth of food would make anyone feel grim - your body can’t process that comfortably. If you are very hungry because you’ve mistakenly undereaten, then try increasing your meals by 20% (experiment) for a couple of days till you feel fine. Your body can adapt and you don’t always need to make it all up, although fine if you eventually do.
I hope some of that is helpful. The main message is be positive - you have done amazingly well, and don’t make a huge deal of having to have a food plan, we all have weak spots.
Finally it’s worth checking with your GP just to get bone density and iron levels monitored.