PHP - Using Variables When Creating A File

<?php
include "config.php";
?>

<?php
require "class.loginsys.php";
$LS=new LoginSystem();
?>

<?php
	   	if( isset($_POST['submit']) ){
	   			$firstname2 = $_POST['firstname'];
	   			$lastname2 = $_POST['lastname'];
	    		$user2	 = $_POST['username'];
	    		$sex2 = $_POST['sex'];
	    		$country2 = $_POST['strCountryChoice'];
	    		$email2 = $_POST['email'];
	    		$pass2	 = $_POST['pass'];
	    		$pass3 = $_POST['pass2'];
	    		$birthdate2 = $_POST['birthdate'];
	    		$created2 = date("Y-m-d H:i:s");
	    		//need to add a lot more validation functions.. AKA Check if email exists and username. Password > 5 chars
	    		if( $user2=="" || $email2=="" || $pass2=='' || $pass3=='' || $firstname2=='' || $lastname2=='' || $sex2=='' || $country2=='' || $birthdate2=='' ){
	     			echo "Fields Left Blank","Some Fields were left blank. Please fill up all fields.";
	     			exit;
	    		}
	    		if( !$LS->validEmail($email2) ){
	     			echo "E-Mail Is Not Valid", "The E-Mail you gave is not valid";
	     			exit;
	    		}
	    		if( !ctype_alnum($user2) ){
	     			echo "Invalid Username", "The Username is not valid. Only ALPHANUMERIC characters are allowed and shouldn't exceed 10 characters.";
	     			exit;
	    		}
	    		if($pass2 != $pass3){
		     		echo "Passwords Don't Match","The Passwords you entered didn't match";
	     			exit;
	    		}
   	 		$createAccount2 = $LS->register($user2, $pass2,
	    			array(
	    				"email" 	 => $email2,
	    				"name" 	 => $firstname2,
	    				"lastname" => $lastname2,
	    				"gender" => $sex2,
	    				"country" => $country2,
	    				"DOB" => $birthdate2,
	    				"created" => date("Y-m-d H:i:s") // Just for testing

	    			)
	    		);
			//$createAccount = $LS->register($firstname,$lastname,$user,$sex,$country,$email,$pass,$birthdate,$created);
	    		if($createAccount2 === "exists"){
	     			echo "User Exists.";
	    		}elseif($createAccount2 === true){
	     			echo "Success. Created account.";
	    		}
	   	}
	   	?>

	/* A function to register a user with passing the username, password and optionally any other additional fields. */
	public function register( $id, $password, $other = array() ){
		if( $this->userExists($id) && (isset($other['email']) && $this->userExists($other['email'])) ){
			return "exists";
		}else{
			$randomSalt	= $this->rand_string(20);
			$saltedPass	= hash('sha256', "{$password}{$this->passwordSalt}{$randomSalt}");
			
			if( count($other) == 0 ){
				/* If there is no other fields mentioned, make the default query */
				//old query: ("INSERT INTO `{$this->dbtable}` (`username`, `password`, `password_salt`) VALUES(:username, :password, :passwordSalt)");
				//new query: ("INSERT INTO `{$this->dbtable}` (`username`, 'email' , `password`, `password_salt` , 'name' , 'lastname' , 'gender' , 'country' , 'DOB') VALUES(:username, :email, :pass, :passwordSalt, :firstname, :lastname, :gender, :country, :DOB)");
				$sql = $this->dbh->prepare("INSERT INTO `{$this->dbtable}` (`username`, `password`, `password_salt`) VALUES(:username, :password, :passwordSalt)");
			}else{
				/* if there are other fields to add value to, make the query and bind values according to it */
				//old query: ("INSERT INTO `{$this->dbtable}` (`username`, `password`, `password_salt`, $columns) VALUES(:username, :password, :passwordSalt, :$colVals)");
				//new query: ("INSERT INTO `{$this->dbtable}` (`username`, 'email' , `password`, `password_salt` , 'name' , 'lastname' , 'gender' , 'country' , 'DOB') VALUES(:username, :email, :pass, :passwordSalt, :firstname, :lastname, :gender, :country, :DOB)");
				$keys	 = array_keys($other);
				$columns = implode(",", $keys);
				$colVals = implode(",:", $keys);
			//l= $this->dbh->prepare("INSERT INTO `{$this->dbtable}` (`username`, `password`, `password_salt`, $columns) VALUES(:username, :password, :passwordSalt, :$colVals)");
				//INSERT INTO MyGuests (firstname, lastname, email)cLUES ('John', 'Doe', 'john@example.com')
				$sql = $this->dbh->prepare("INSERT INTO `{$this->dbtable}` (username,email,password,password_salt,name,lastname,created,gender,country,DOB) VALUES ('$username2','$email2','$pass2','$saltedPass','$firstname2','$lastname2','$created2','$gender2','$country2','$birthdate2')");
				print($sql);
				foreach($other as $key => $value){
					$value = htmlspecialchars($value);
					$sql->bindValue(":$key", $value);
				}
			}
			/* Bind the default values */
			$sql->bindValue(":username", $id);
			$sql->bindValue(":password", $saltedPass);
			$sql->bindValue(":passwordSalt", $randomSalt);
			$sql->execute();
			return true;
		}
	}