And the anime only does about 90? Is that correct?

I don't know. I've never seen the anime. xD

[Spoiler Alert!!] At the end of the anime, more or less everyone is dead besides the main character and Gantz has put him in a game with new people except he is the target. He ends up killing everyone.

How far is that in the manga? I know sometimes they add their own endings. Does this scene even happen in the manga?