Anorexia Recovery & Treatment

I’m thinking about not exercising today. But I just got my new meal plan from my nutritionist for anorexia recovery and so for the first time I’m going to be eating probably twice the calories that I usually do. Should I take the day off or will I gain weight?

When i entered recovery for anorexia 4 weeks ago i was 5′8 118 pounds and they put me on meal plan c (2000 calories) because i needed to gain weight and because i was exercising alot. A day after being told i needed to follow that meal plan, i was told by my doctor that i could only go for walks because my heart rate was 41. now, 4 weeks later, i am at 122 lbs and they just changed my meal plan to meal plan b (maintain weight) because i still cannot exercise; not because of my heart, but because i was over exercising last week when i was told by my doctor it was not safe to exercise. My question is, now that i am on meal plan b (1800 calories) and not exercising wont i gain weight? why would they put me on a meal plan to maintain weight if i am going to gain weight from it?

My bmi is 14.8, I’m 16, and 5″3.5
i’d like it to include liquids… i can blend up complan or milkshake/smoothie/nestle build up supplements.
recommendations please.