Not displaying the error messages in PHP - php

Question

If there are any errors while registration or login into the sit then it is not displaying the error message just printing the variable.Here is the code.Tried by doing echo as well but it is also not working.Tried with storing the result in a variable and displaying the message but still not worked.
<?php
include 'includes/db.php';
$match = '';
if(isset($_POST['submit_user']))
{
$email = $_POST['email'];
$check=mysqli_query($conn,"select * from users where user_email='$email'");
$checkrows=mysqli_num_rows($check);
if($checkrows>0)
{
$msg = "Email Already Exists";
header('Location:registration.php?msg=$msg');
}
else
{
if($_POST['password'] == $_POST['con_password'])
{
$ins_sql = "INSERT INTO users (first_name, last_name, user_email, user_password, username) VALUES ('$_POST[first_name]', '$_POST[last_name]', '$_POST[email]', '$_POST[password]', '$_POST[username]')";
$run_sql = mysqli_query($conn,$ins_sql);
}
else
{
$match = '<div class="alert alert-danger">Password doesn&apos;t match!</div>';
}
}
}
?>
<form class="form-horizontal" action="registration.php" method="post" role="form">
<div class="body">
<div class="row clearfix">
<div class="col-sm-6 col-xs-12">
<div class="form-group">
<div class="form-line">
<input type="text" class="form-control" placeholder="First Name" name="first_name" id="first_name" onkeypress="return checkSpcialChar(event)" required>
</div>
</div>
</div>
<div class="col-sm-6 col-xs-12">
<div class="form-group">
<div class="form-line">
<input type="text" class="form-control" placeholder="Last Name" name="last_name" id="last_name" required>
</div>
</div>
</div>
</div>
<div class="row clearfix">
<div class="col-sm-12">
<div class="form-group">
<div class="form-line">
<input type="text" class="form-control" placeholder="Enter Your Email" name="email" id="email" required>
</div>
</div>
</div>
<div class="col-sm-12">
<div class="form-group">
<div class="form-line">
<input type="password" class="form-control" placeholder="Password" name="password" id="password" required>
</div>
</div>
</div>
<div class="col-sm-12">
<div class="form-group">
<div class="form-line">
<input type="type" class="form-control" placeholder="Confirm Password" name="con_password" id="con_password" required>
</div>
</div>
</div>
<div class="col-sm-12">
<div class="form-group">
<div class="form-line">
<input type="text" class="form-control" placeholder="Enter Username" name="username" id="username">
</div>
</div>
</div>
<div class="col-sm-12">
<div class="form-group drop-custum">
<select class="form-control show-tick" name="user_role" id="user_role" required>
<option value="">-- Select User role --</option>
<option value="admin">Admin</option>
<option value="employee">Employee</option>
</select>
</div>
</div>
<div class="col-sm-12">
<button type="submit" class="btn btn-raised g-bg-cyan" name="submit_user" id="subject">Submit</button>
<button type="submit" class="btn btn-raised">Cancel</button>
</div>
<span>
<?php if(isset($_GET['msg']))
echo $_GET['msg'];
?>
</span>
</div>
</div>
</form>