Keep user login error in modal box

<?php
	require('db.php');
	session_start();
    // If form submitted, insert values into the database.
    if (isset($_POST['username'])){
		
		$username = stripslashes($_REQUEST['username']); // removes backslashes
		$username = mysqli_real_escape_string($con,$username); //escapes special characters in a string
		$password = stripslashes($_REQUEST['password']);
		$password = mysqli_real_escape_string($con,$password);
		
	//Checking is user existing in the database or not
        $query = "SELECT * FROM `users` WHERE username='$username' and password='".md5($password)."'";
		$result = mysqli_query($con,$query) or die(mysqli_error());
		$rows = mysqli_num_rows($result);
        if($rows==1){
			$_SESSION['username'] = $username;
			header("Location: index.php"); // Redirect user to index.php
            }
            else{
	echo "<div class='form'><h3>Username/password is incorrect.</h3><br/>Click here to <a href='login.php'>Login</a></div>";
				}
    }else{
?>
<div class="container">
    <div class="col-lg-3 mx-auto"></div>
    <div class="col-lg-4 mx-auto"></div>
    <div class="col-lg-3 mx-auto"></div>
    <div class="row vertical-center-row">
        <div class="col-lg-5 mx-auto"><br/>
            <h3 class="text-center">LOGIN HERE</h3>  
            <div class="form">
                <form action="" method="post" name="login" style="text-align:center">
                    <input class="unbox" type="text" name="username" placeholder="Username" required /><br/><br/>
                    <input class="unbox" type="password" name="password" placeholder="Password" required /><br/><br/>
                    <input name="submit" type="submit" value="Login" />
                </form>
                <p>Not registered yet? <a href='registration.php'>Register Here</a></p>
                <br /><br />
            </div>
        </div>
    </div>
</div>
 
<?php } ?>

<?php
	require('db.php');
	session_start();
    // If form submitted, insert values into the database.
    if (isset($_POST['username'])){
		
		$username = stripslashes($_REQUEST['username']); // removes backslashes
		$username = mysqli_real_escape_string($con,$username); //escapes special characters in a string
		$password = stripslashes($_REQUEST['password']);
		$password = mysqli_real_escape_string($con,$password);
		
	//Checking is user existing in the database or not
        $query = "SELECT * FROM `users` WHERE username='$username' and password='".md5($password)."'";
		$result = mysqli_query($con,$query) or die(mysqli_error());
		$rows = mysqli_num_rows($result);
        if($rows==1){
			$_SESSION['username'] = $username;
			header("Location: index.php"); // Redirect user to index.php
            }
            else{
	<pre><script type="text/javascript">
    $(document).ready(function(){
        $("#myModal").modal('show');
    });
</script>

<!-- Modal -->
<div id="myModal" class="modal fade" role="dialog">
  <div class="modal-dialog">

    <!-- Modal content-->
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal">×</button>
        <h4 class="modal-title">Modal Header</h4>
      </div>
      <div class="modal-body">
        <p>User name/password is wrong</p>
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
      </div>
    </div>

  </div>
</div>