I lost 3kg pretty quickly in the first couple of weeks, but as of yesterday I gained it all back, even though I only had a single meal on one day that took me over my calorie deficit.
Don't pay too much attention to weight. Weight depends on a lot of factors.
For instance the moment you weigh yourself. And when you drink a lot of water you also weigh more. And muscles also weigh more than fat. Just pay attention to what you eat; less sugar, less fat and less processed food.
You'd better measure your fat percentage or if you can't do that for instance measure your waist.