Android Studio – set cardview width and margins

I have an application with a recyclerview that contains several cardviews. And the thing is that I don’t know how to set the width of the cardview so that it occupies the entire width of the screen. I also don’t know how to make each cardview separate from the previous one and the next one. I have added margins to all the elements but the cardviews are displayed together. This is a screenshot of what the layout looks like:screenshot

and this is the code of the two layouts. First the one from the mainactivity that contains the recyclerview:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">
    <include layout="@layout/toolbar"/>
    <Button
        android:id="@+id/escanearCodigo"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Escanear codigo"
        android:layout_weight="1"
        />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="20dp"
        />
</LinearLayout>

and this is the one for each item of the recyclerview (the one that contains the carviews):

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/card_view"
    android:layout_margin="20dp"
    app:cardBackgroundColor="#81C784"
    app:cardCornerRadius="12dp"
    app:cardElevation="3dp"
    app:contentPadding="4dp"
    >
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:layout_margin="12dp"
        >
            <TextView
                android:id="@+id/idCodigo"
                android:layout_height="wrap_content"
                android:layout_width="match_parent"
                android:layout_margin="5dp"
                />
            <TextView
                android:id="@+id/idNombre"
                android:layout_height="wrap_content"
                android:layout_width="match_parent"
                android:layout_margin="5dp"
                />
        </LinearLayout>
</androidx.cardview.widget.CardView>