Whenever I enter / setworldspawn at a position, I spawn at a random other location. I just do not understand. Hope someone of you can help me.
/ setworldspawn
only sets the spawn for new players and for players who have not yet used beds. What you are looking for is:
/ Spawnpoint
This will allow you to change your spawn point. With
/ gamerule spawnRadius 0
Can you make that the world spawn is really on the block exactly defined and not in a radius outside.
Hope that helps you!