Let me think...
8 worlds, so each world is one place, but with say, about 10 missions on that. That's only 80 stars. It would take about 24 worlds to get exactly 240 stars. There's bonus levels too, so say 22 worlds, with 20 bonus stars (SM64 had 15.) Give or take, it'll be like that. Of course there will probably be secret stars too...