Your TextView Attributes need to be something like,
<TextView ...
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_vertical|right" ../>
Now, Description why these need to be done,
android:layout_width="match_parent"
android:layout_height="match_parent"
Makes your TextView to match_parent or fill_parent if You don't want to be it like, match_parent you have to give some specified values to layout_height so it get space for vertical center gravity. android:layout_width="match_parent" necessary because it align your TextView in Right side so you can recognize respect to Parent Layout of TextView.
Now, its about android:gravity which makes the content of Your TextView alignment. android:layout_gravity makes alignment of TextView respected to its Parent Layout.
Update:
As below comment says use fill_parent instead of match_parent. (Problem in some device.)