Rasberry pi

I am working on an application using a Rasberry PI (linux).  It is working well.  But  I am working on a 5" touch screen that is 800x600.  The problem is that standards sizes of everything is way too small.  For example I have an alert window that has a combobox and cancel/save/ buttons.  The default sizes of the buttons and the comboboxes are too small for my large fingers.

I made the window larger by doing this getTopLevelWindow(1)->setSize(600,400); on the AlertWindow.  But the items within are still too small.

Is there a way to scale everything larger ? 

Desktop::setGlobalScaleFactor ?