G'day to you guys

I'm trying to make a GridLayout with 3 columns and some rows (not known yet), just like this tutorial but with button filling each box of the GridLayout. I use pictures for each button, then problems come out. The I set the grid layout to match_parent and the pics (buttons) to wrap_content, but the right side of the grid layout goes beyond the parent. Anyone know how to fix this? Thanks for your answers.

Here's the xml code:

<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="@drawable/background"
    android:orientation="vertical"
    tools:context="com.endonezyam.multipleactivities.MainActivity">

<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent">

            <GridLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:padding="10dp"
                android:columnCount="3">

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:onClick="buttonClicked"
                    android:id="@+id/button1"
                    android:background="@drawable/a"
                    android:layout_columnWeight="1" />

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:onClick="buttonClicked"
                    android:id="@+id/button2"
                    android:background="@drawable/b"
                    android:layout_columnWeight="1" />

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:onClick="buttonClicked"
                    android:id="@+id/button3"
                    android:background="@drawable/c"
                    android:layout_columnWeight="1" />

            </GridLayout>

</ScrollView>

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/istanbul"
        android:baselineAlignBottom="false"
        android:layout_gravity="bottom"
        android:adjustViewBounds="true"/>

</FrameLayout>