You really need to eat very cautiously, as too much too soon, could be detrimental.
Givne your age, you would be also advised to perhaps seek alternative advise to this. This is NOT necessarily what you should do, but I believe it is okay for you to try what I am suggesting.
I would suggest a 6 meal a day strategy, to allow the body to get used to eating in a normal way, but keep it low calorie for now, incase the body isn't ready for 300+ calories a pop, which undoubtedly it won't be.
You shouldn't exercise either at the moment, becasue you might stimulate the Thyroid too much, which wouldn't be good in your current state, and you might have bone density issues, which might increase risk of Fractures, or things like Dislocation or Subluxation, (partial Dislocation), if you stress the body out with Cardio or weights.
Plus you might be in a state of Osteopenia, a T-score test would identify this, which would be the case if you rated between -1 and -2.5.
So I'd avoid exercise for the mean time.
I would limit you at the moment to around 60 calories a meal.
N:B: THIS IS ONLY FOR THE FIRST WEEK.
So this is what I would suggest as a possible schedule
Meal 1. 1 scrambled Egg White, with 1tspn of Skimmed milk beaten in + 1/2 Apple (60 calories approx in total). Give the Apple 10-15 minutes to digest, then eat the Whites.
Meal 2. 1/4 Skinless Chicken Breast, 1 Large Tomato + 1 Lettuce Leaf. (60 calories approx).
Meal 3. 1 Cup Green Beans + 2 OZ Skimmed Milk. (60 calories approx).
Meal 4. 1/4 Skinless Chicken Breast, 1 Large Tomato + 1 Lettuce Leaf. (60 calories approx).
Meal 5. 1 Cup Green Beans + 1 Small Tomato. (60 calories approx).
Meal 6. 1/4 Skinless Chicken Breast + 1 regular sized Carrot. (60 calories approx).
You could experiment with the Chicken, by adding a tiny amount of Celtic Sea Salt and maybe a little Lemon Juice for flavouring.
360 calories in total.
As I say this is only for a week, and I've kept your choices simple, so it's not to difficult to follow.
In a weeks time, when you're body has had chance to adapt to this, then calories could go up a bit more, and maybe a bit of variety in choice.
You need to make sure you're taking things slowly on this, incase too much too soon is detrmiental.
As I say, if you're concerned or not sure, seek alterntive help.