my linear layouts don't go into the center!

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="james.ribbit.loginActivity"
    android:clickable="false"
    style="@style/AuthBackground">

    <include layout="@layout/auth_common"/>

    <LinearLayout
        android:id="@+id/editTextLayout"
        style="@style/AuthFieldContainer"

        android:layout_width="400dp"
        android:layout_centerVertical="true">

        <EditText
            android:id="@+id/usernameField"
            style="@style/Authedittext"

        android:hint="@string/username_hint"
        />

        <EditText
            android:id="@+id/passwordField"

            android:hint="@string/password_hint"
            style="@style/Authedittext">
            <requestFocus/>
        </EditText>

    </LinearLayout>

    <Button
        android:layout_width="400dp"
        android:layout_centerVertical="true"
        android:text="@string/login_button_label"
        android:id="@+id/loginButton"
        style="@style/AuthButton"
        android:layout_below="@+id/editTextLayout"
        android:layout_alignParentLeft="true"/>


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/sign_up_text"
        android:id="@+id/signUpText"
        android:textColor="@android:color/white"
        android:layout_below="@+id/loginButton"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="10dp"/>

</RelativeLayout>