ชื่อไฟล์ txt ไม่ขึ้นคะ ใครรู้วิธีแก้ ช่วยตอบหน่อยนะคะ

<?php
<?php
session_start();
// Check If session available
if (isset($_SESSION['userName']) && 
    isset($_SESSION['password'])) 
    {
      
    $UserName = $_SESSION['userName'];
    $Password = $_SESSION['password'];
    
        $FirstName = $_POST['fname'];
        $LastName  = $_POST['lname'];
        $DateBook  = $_POST['datebook'];
        $Time       = $_POST['time'];
        $GuestNum  = $_POST['guest_num'];
    
    $Dir = "Booking/";
    if  (!file_exists($Dir)) //Check if file not exists.
        mkdir($Dir, 0777); //Create books directory. 
        $BookFolder = $Dir . $FirstName . ".txt";
        $Booking = fopen($BookFolder, "a+");
        chmod ($Dir . $FirstName . ".txt", 0777);
        
        
        if (is_writable($BookFolder)) {
        if (fwrite($Booking, $DateBook . "\n" . $FirstName . "\n" . 
                   $LastName . "\n" . $Time . "\n" . $GuestNum . "\n")) {
            echo "<p>Booking Completed. Thank you for choosing Taley Restaurant.<br/>
            <form action='menu.html'method='post'>
            <input type ='hidden' name ='userName' value ='$UserName'/>
            <input type ='hidden' name ='password' value ='$Password'/>
            <input type ='hidden' name ='PHPSESSID' value ='<?php echo session_id() ?>'/>
            <input type='submit' value='Menus page'/></form></p>";
            fclose($Booking);
            }
            
            else
                echo "<p>cannot write record to file.</p>";
    }
    }
    
else {
    echo "you have to <br/><a href='cust_login.html'>Log in</a>";
}
?> 
?>