I'm making an app using Android Studio as my IDE and Genymotion as my emulator and I see a difference between the preview of Android Studio and the real output of Genymotion but I wonder which one trust.
Both of them are using a 768 x 1280 phone but it seems the one in Genymotion is bigger.
Your dpi settings in both are different.
Android Studio is xhdpi. Genymotion is 160 dpi which mdpi (default). In order to properly compare, you'll have to set both the same pixel density and screen resolution.