HI my code is no longer functioning to limit the amount of lines in SQL it should limit 300 its 900

$result = OpenPDO($conn,"SELECT COUNT(`datetime`) FROM `played_songs` ORDER BY `datetime` ASC",$_query,"");

$row = $result->fetch();

$n = $row["COUNT(`datetime`)"] - 300;

     

if ($n > 1) {       

 $q = OpenPDO($conn,"SELECT `datetime` FROM `played_songs` ORDER BY `datetime` ASC",$_query,"");

 while ($n) {

  $r = $q->fetch();

  $id = $r["datetime"];

  OpenPDO($conn,"DELETE FROM `played_songs` WHERE `datetime`=?" ,$_execute,$id);

  $n--;

 }