I have the same problem!! This is really anoying issue. When i test app with companion everything is ok, well set, icons buttons fonts… But when i build and install app, whole different story. Everything is smaller… I have never had this problem before, this is new. Strange thing is, when i build some of my old projects, same thing happens. But before 2 months those apps where fine builded!
try to set the property Sizing of Screen1 to responsive
see also the documentation User Interface
Sizing
If set to responsive (the default), screen layouts will use the actual resolution of the device. See the documentation on responsive design in App Inventor for more information. If set to fixed, screen layouts will be created for a single fixed-size screen and autoscaled.
Note: This property appears on Screen1 only and controls the sizing for all screens in the app.
Taifun
Trying to push the limits! Snippets, Tutorials and Extensions from Pura Vida Apps by 
Taifun.