Command 0 not sizing properly.

[kents72809256]

When I push command 0 on my imac, the image is not sizing properly.  It is too big.  I have to use command - to drop it down one more notch so image won't float.  How do I get command 0 to size properly?

[c.pfaffenbichler]

Could you please post a screenshot (edited; sorry, you were talking about »Fit on Screen«, not »100%«) with the pertinent Panels (Toolbar, Layers, Channels, Options Bar, …) visible? 

Have you verified that the Shorcut has not been changed (Edit > Keyboard Shortcuts)? 

[kents72809256]

yes the fit on screen is the issue. Command 0 leaves image larger than screen.

[c.pfaffenbichler]

Have you verified that the Shorcut has not been changed (Edit > Keyboard Shortcuts)? 

What have you done for all-purpose trouble-shooting so far?
Restoring Preferences after making sure all customized presets like Actions, Patterns, Brushes etc. have been saved might be a good starting point:
https://helpx.adobe.com/photoshop/kb/basic-trouble-shooting-steps.html
https://helpx.adobe.com/photoshop/using/preferences.html