Remove margin to Button. Android Studio

I have a Button defined

<Button
   android:id="@+id/btnCuentaNueva"
   android:layout_width="match_parent"
   android:layout_height="@dimen/btn_height"
   android:text="No tenés una cuenta? Registrate"
   android:theme="@style/RButtonGris" />

and a style

<style name="RButtonGris" parent="Theme.AppCompat.Light">
    <item name="colorButtonNormal">@color/colorGris</item>
    <item name="colorControlHighlight">@color/colorHover</item>
    <item name="android:textColor">@color/colorNegro</item>
    <item name="android:textAllCaps">false</item>
    <item name="android:textSize">18dp</item>
    <item name="android:fontFamily">@font/grlight</item>
</style>

The problem is that I generate a margin although I have not declared it and my intention is to cover the entire width of the screen, I leave an image to show better

Thank you very much in advance