Android layout for images

My requirement is to bring 3 small circles in the bottom of the screen in the middle position.. So,I have done this:--

footer.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:padding="15dip"
android:background="@color/d_blue"
android:layout_gravity="bottom"
android:orientation="vertical" >
<Button android:layout_height="wrap_content"
     android:layout_width="wrap_content"
android:id="@+id/btn1"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:background="@drawable/rounded" />
  <Button android:layout_height="wrap_content"
       android:layout_width="wrap_content"
android:id="@+id/btn2"
android:layout_toRightOf="@id/btn1"
android:layout_marginLeft="5dip"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:background="@drawable/rounded" />
 <Button android:layout_height="wrap_content" android:layout_width="wrap_content"
android:id="@+id/btn3"
android:layout_toRightOf="@id/btn2"
android:layout_marginLeft="5dip"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:background="@drawable/rounded" /> </RelativeLayout>

and @drawable/rounded.xml is:--

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://ift.tt/nIICcg" 
android:shape="oval" >
<gradient android:startColor="@color/white" android:endColor="@color/white"
    android:angle="270"/>
<stroke android:color="@color/l_blue" android:width="1dp" />

But this are not in the middle position..How can I get that 3 small circles in a middle position??