A room becomes yours through the life lived inside it.

Nothing about a room belongs to you at first. It becomes yours through sleeping badly in it, laughing in it, working late in it, knowing which floorboard creaks. Possession here is not legal, it is accumulated, and no amount of arranging can substitute for time spent living.

If a space still feels borrowed, the answer is usually more use rather than more effort. Do the ordinary things there. Ownership in this sense arrives quietly and you tend to notice it only in retrospect.