The following xml will center TextView within RelativeLayout.
android:layout_centerInParent to center the TextView, android:gravity make sure the text is not left aligned.
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="200dp">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:layout_centerInParent="true"
android:text="Line 1\nLine 2"
/>
</RelativeLayout>