You can use the below code to change the button to Left side.
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:map="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/map"
android:name="com.google.android.gms.maps.SupportMapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.zakasoft.mymap.MapsActivity" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="left|top"
android:text="Send"
android:padding="10dp"
android:layout_marginTop="20dp"
android:paddingRight="10dp"/>
</fragment>