how to set equal margin between recyclerview items

See this Image

I achieved the current margin from xml layout but its not same through all four sides.

How to get equal margin

My current xml layout

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="300dp">

<ImageView
    android:id="@+id/iv_photo"
    android:layout_width="match_parent"
    android:layout_height="300dp"
    android:layout_marginEnd="6dp"
    android:layout_marginTop="6dp"
    android:adjustViewBounds="true"
    android:background="@color/colorPrimary"
    android:foreground="?android:attr/selectableItemBackground"
    android:scaleType="fitXY" />

</RelativeLayout>