XML error -- Extra content at the end of the document

I'm getting an "Extra content at the end of the document" error here. I believe it has something to do with there being more than one document root. How may I fix this please? Thanks.

<?php
      $key = $_GET['key'];

      // Start XML file, create parent node
      $dom = new DOMDocument("1.0");
      $node = $dom->createElement("markers");
      $parent = $dom->appendChild($node);
      //$dom->formatOutput = true;

       // Opens a connection to a MySQL server
       $connection=mysql_connect ('localhost', 'wordpressdbadmin', 'wordpressdbpass');
       if (!$connection)
       {
       die('Not connected : ' . mysql_error());
        }
        else
    {
       $db_selected = mysql_select_db(geocodeindex3, $connection);
           $query = "SELECT locations.name, locations.add, locations.lat, locations.long FROM locations where id=".$key.";";
           $result = mysql_query($query);

           header("Content-type: text/xml");

       while ($row = mysql_fetch_array($result))
          {
             // ADD TO XML DOCUMENT NODE
              $node = $dom->createElement("marker");
              $newnode = $parent->appendChild($node);
              $newnode->setAttribute("name", $row['name']);
              $newnode->setAttribute("address", $row['add']);
              $newnode->setAttribute("lat", $row['lat']);
              $newnode->setAttribute("lng", $row['long']);
       }
          echo $dom->saveXML();
     }
?>