what I am doing wrong,

i'm also placing myself on the "watering during light cycle" side.. Imagine it this way: have you ever tried burning things with a magnifying glass in the sun? That's basically what you're doing with water-droplets on the leaf under a grow-light. So i would a) recommend to water around the plant (this also will be important once you start feeding the plant) and b) preferably just before the lights go out. Point b) will help if there are still water-droplets on the plant, and keep it from burning in. Other than that, i hope you're NOT yet giving her any nutrients, right?

Bro, this looks like a thermal burn. If you're spraying the plant with water during the lighting period - stop doing that, it's the cause of the burn. You can only spray at the moment the lights go off or after, but not while the lamps are on. Good luck, bro! 👋 👍

The problem is in your first picture, when u are watering, u are watering the leaves. U should NEVER water the leaves because if u have a nutrient solution in there it will burn through the leaves, or when u have strong lights it will make these kinds of burns that u are seeing. U should allways try to water around the plant (like 5cm away from the stem in a circular motion) to stimulate the roots to go where the water is.