Android : Creating and positioning a Floating Action Button

I'm trying to add a FAB to the bottom of a card view, like in this app:

The button does show up, but it has a wrong height, and it should be a bit lower. I'm using Android Material Design Library. Here are my files:

colors.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="colorPrimary">#3F51B5</color>
    <color name="colorPrimaryDark">#303F9F</color>
    <color name="colorAccent">#FFEB3B</color>
    <color name="colorAccentDark">#FBC02D</color>
</resources>

activity_main.xml

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:materialdesign="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"

    tools:context=".MainActivity">

    <include
        android:id="@+id/toolbar"
        layout="@layout/toolbar" />
    <LinearLayout
        xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:id="@+id/main_content"
        android:layout_below="@id/toolbar">

        <android.support.v7.widget.CardView
            xmlns:card_view="http://schemas.android.com/apk/res-auto"
            android:id="@+id/stop_card"
            android:layout_gravity="center"
            android:layout_width="match_parent"
            android:layout_height="100dp"
            android:layout_marginTop="5dp"
            card_view:cardCornerRadius="4dp">

            <LinearLayout
                android:orientation="vertical"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:paddingLeft="10dp"
                android:paddingTop="5dp"
                android:paddingRight="10dp"
                android:paddingBottom="5dp">

                <TextView
                    android:id="@+id/label_stop"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:text="Fermata"
                    android:textSize="25sp"
                    android:textStyle="bold"
                    android:singleLine="true" />

                <EditText
                    android:id="@+id/edit_stop"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:inputType="number"
                    android:ems="10"
                    android:layout_gravity="end" />

                <com.gc.materialdesign.views.ButtonFloat
                    android:id="@+id/buttonFloat"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:background="#1E88E5"
                    materialdesign:animate="true"
                    materialdesign:iconDrawable="@android:drawable/ic_menu_search" />
            </LinearLayout>
        </android.support.v7.widget.CardView>
    </LinearLayout>
</RelativeLayout>

This is what I'm getting in Android Studio preview:

It's almost right, but it should be higher in order to contain the drawable and should be on the other end of the card view, a bit lower.