Android NumberPicker Plus/Minus Signs Not Centered

Question

I created a dialog with a NumberPicker, however I can't center plus and minus signs. Here is my code and the image, any help is appretiated!

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content" >

<NumberPicker
    android:id="@+id/numberPicker1"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginBottom="20dp"/>

<Button
    android:id="@+id/cancel"
    android:layout_width="150dp"
    android:layout_below="@+id/numberPicker1"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:text="Cancel" />

<Button
    android:id="@+id/set"
    android:layout_width="150dp"
    android:layout_height="wrap_content"
    android:layout_below="@+id/numberPicker1"
    android:layout_alignParentRight="true"
    android:text="Set" />

/RelativeLayout>