我正在插入准备好的语句插入数据，但是当我插入检查重复它给我错误如何解决

if(isset($_POST['submit'])){
//echo "Did you click me";

$username = mysqli_real_escape_string($conn,$_POST['username']);

$sql  = "SELECT count(1) FROM user_register WHERE username = ?";
$stmt = $conn->prepare($sql);
$stmt->bind_param("s", $username);
$stmt->execute();
$stmt->bind_result($found);
$stmt->fetch();
if ($found)
{
echo "Email is already exist";
//die;
}
else
{
    echo"Debug";


    $insert_data = $conn->prepare("INSERT INTO  user_register (first_name, last_name, mobile,username,user_password) VALUES (?, ?, ?,?,?)");
$insert_data->bind_param("ssiss", $first_name, $last_name, $mobile,$username,$user_password);
print_r($insert_data);
die;
// set parameters and execute
//$fname=ucfirst($_POST['first_name']);
$first_name = mysqli_real_escape_string($conn,$_POST['first_name']);

$last_name = mysqli_real_escape_string($conn,$_POST['last_name']);
$mobile = mysqli_real_escape_string($conn,$_POST['mobile']);
$username = mysqli_real_escape_string($conn,$_POST['username']);
$user_password = mysqli_real_escape_string($conn,$_POST['user_password']);

    if($insert_data->execute()){
        echo "Inserted";
    }
    else{
        echo"Error";
    }
    $insert_data->close();
        $conn->close();

}


}

I want check email duplicacy in my code with prepared statement and if not available insert otherwise show error but when i check email it is working but it is not inserting new user with new email please help me.

ERROR:Fatal error: Call to a member function bind_param() on boolean in C:\wamp64\www\vaibhav\prepared-statement with session\insert_data.php on line 277

if(isset($_POST['submit'])){
//echo "Did you click me";

$username = mysqli_real_escape_string($conn,$_POST['username']);

$sql  = "SELECT count(1) FROM user_register WHERE username = ?";
$stmt = $conn->prepare($sql);
$stmt->bind_param("s", $username_stmt);
$username_stmt = $username;
$stmt->execute();
$stmt->bind_result($found);
$stmt->fetch();
 if ($found)
 {
   echo "Email is already exist";
   //die;
 }
else
{
   echo"Debug";
}

you missed one line of code. Hope this works