Android Layout Background Won't fit to scale -

i'm new android programming , i'm having trouble setting main layout's background since won't scale.

there white border around background wont go away background cannot fit entire screen. loaded image res/drawable-xhdpi folder , wrote code below.

this activitymain code:

<linearlayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/layout" android:background="@drawable/background" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" android:gravity="center_horizontal" android:layout_margin="@dimen/activity_horizontal_margin"  > 

==>> there white border around background  

this due layout_margin, check out removing android:layout_margin="@dimen/activity_horizontal_margin"

and background fit .