Why cant I get my screen centered on Macbook?

I’m not sure what you’re talking about exactly, but try holding down “ctrl” and dragging two fingers down your trackpad.

Is it large enough? Or do you not want it to take up the whole screen? Try pushing the green circle button in the top left.

More info needed.

If u had a few screens/apps open at onceand u activate “all windows” button, it will show them all on desktop only much smaller. Is that what is going on?
To fix goto Apple menu, preferences, dashboard/expose and then assign or un-assign F keys.
Goodluck.

I’m going to guess here that you’re talking about the window itself?