You can keep playing NG+ to farm up your world tendency. 

If you play online the servers will reset your world tendency to whatever the current average is at the time. If you want a specific WT it's best to play offline.

I've been looking to get world 3 to PWWT, but I've already killed BP Rydell and left so I don't have PBWT anymore.  Looking online people keep saying that to get PWWT I need to kill Rydell, the primevil and the boss in the same run to get PWWT.  Does this mean the only way to get PWWT is to pvp or coop?

PWWT World 3