Underweight? 🤔

So in the past 2-3 days I’ve put myself in an intense weight gain diet. I am 1,60m in height and weight around 44kg, and according to the BMI scale I’m considered underweight.

Look by yourself:

There’s clearly ribcage showing and a quite big thigh gap, and also slender hands and legs. Bearing in mind I’m an 18 year old though, I feel like this is not a healthy image. It’s not normal having the body of a child at my age, comparing to my friends who look like women.

This is a body visualizer of all my info plotted:

My goal is to gain some weight and sign up to the gym next month. But I need tips. What do you think?