Align LinearLayout inside a RelativeLayout issue – Photoshop

How can i align the “LoginBox” LinearLayout to its parent (that is a RelativeLayout) both at left/right and bottom? I tried to insert:

 android:layout_alignParentBottom="true"
 android:layout_alignParentLeft="true"
 android:layout_alignParentRight="true"

but it doesn’t do the trick! Infact the linearlayout is not properly aligned to the margin of the screen! 🙁

This is my XML code:

<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"
    android:background="@drawable/sfondologin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

<ImageView
    android:id="@+id/imageView1"
   android:layout_width="200dp"
            android:layout_height="200dp"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    android:src="@drawable/stemmatrasparente" />

<LinearLayout
    android:id="@+id/LoginBox"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentRight="true"
    android:orientation="vertical" >

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <EditText
            android:id="@+id/usernametxt"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_alignParentRight="true"
            android:background="@drawable/sfondobuttonedittext"
            android:drawableLeft="@drawable/usericon"
            android:ems="10"
            android:gravity="center_horizontal|center"
            android:paddingLeft="15dp"
            android:imeOptions="actionNext"
            android:singleLine="true"
            android:textSize="18dp"
            android:typeface="sans" >

            <requestFocus />
        </EditText>

    </RelativeLayout>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="0.18" >
    </RelativeLayout>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center" >

        <EditText
            android:id="@+id/passwordtxt"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_alignParentRight="true"
            android:background="@drawable/sfondobuttonedittext"
            android:drawableLeft="@drawable/lockicon"
            android:ems="10"
            android:gravity="center_vertical|center"
            android:inputType="textPassword"
            android:paddingLeft="15dp"
            android:imeOptions="actionDone"
            android:textSize="18dp"
            android:typeface="sans" />

    </RelativeLayout>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="0.29" >

        <TextView
            android:id="@+id/forgotpass"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentRight="true"
            android:layout_alignParentTop="true"
            android:text="Dimenticato la password?"
            android:textColor="@color/white"
            android:textColorHint="@color/white"
            android:textSize="@dimen/value12dp" />

    </RelativeLayout>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <Button
            android:id="@+id/loginbtn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_alignParentRight="true"
            android:layout_alignParentTop="true"
            android:background="@drawable/sfondobuttonlogin"
            android:text="Login"
            android:textColor="@color/white" />

    </RelativeLayout>

    <Button
        android:id="@+id/registerbtn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|center|end"
        android:background="@drawable/sfondobuttonrb2"
        android:text="Registrati"
        android:textColor="@color/white" />

</LinearLayout>
<RelativeLayout
    android:layout_width="wrap_content"
    android:layout_height="fill_parent"
    android:layout_gravity="left"
    android:layout_weight="0.01" 
    android:background="#00000000">
</RelativeLayout>

</RelativeLayout>

Thank you in advance!

EDIT:
The first screen is what i have now! While the second, edited with photoshop (sorry), is what i want to get!