My water weight won't go away

I accidentally over ate end of last week and gained 1.5kg after. I thought that its probs just water weight that should be gone by morning. But now it's been 6 days and none of that weight is gone. I even got back on track and hydrated a lot and everything. But not even one single gram of the weight is gone.

Usually whenever I gain water weight, it's always gone within the next morning or 2 days max.

I'm really scared. Does that mean I gained permanent weight? If it was really water weight, shouldn't it have been gone by now? What am I doing wrong