Singleton pattern on simultaneous connections

I'm developing a project and made a class in the Singleton pattern to connect to the database:

<?
    class Conexao extends PDO {

        private static $instancia;

        public function __construct($dsn, $username = "", $password = ""){
            parent::__construct($dsn, $username, $password, array(
                PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
                PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES utf8"
            ));
        }

        public function prepare($statement, $options = NULL){
            if (!isset($options))
                $options = array();
            $options += array(
                PDO::ATTR_STATEMENT_CLASS => array('Query')
            );

            return parent::prepare($statement, $options);
        }

        public static function getInstance(){
            if (!isset(self::$instancia)){
                try{
                    self::$instancia = new Conexao("mysql:host=localhost; dbname=meu_banco",
                        "meu_usuario", "minha_senha");
                } catch (Exception $e) {
                    throw new Exception("Ocorreu um erro ao conectar!<br />".$e->getMessage());
                }
            }

            return self::$instancia;
        }
    }

    class Query extends PDOStatement{
        function execute($bound_input_params = NULL): bool{
            try{
                return parent::execute($bound_input_params);
            } catch (PDOException $e){
                throw new Exception("
                    Query: ".$this->queryString."<br />
                    (".$e->getCode().") ".$e->getMessage()."<br />
                ");
            }
        }

    }
?>

At some point I had to make a transaction to guarantee the execution of multiple scripts , so I did the following:

<?
    function salvar(){
        $this->validar();

        $conn = null;
        try{
            $conn = Conexao::getInstance();

            $conn->beginTransaction();

            $sql = "";
            if ($this->id == 0){
                $sql = "
                    INSERT INTO 'PedidoCompra' ('idFormaPagamento', 'idFornecedor', 'dataPedido')
                    VALUES (:idFormaPagamento, :idFornecedor, NOW())
                "; 
            } else{
                $sql = "
                    UPDATE 'PedidoCompra' SET
                    'idFormaPagamento' = :idFormaPagamento, 'idFornecedor' = :idFornecedor
                    WHERE 'idPedidoCompra' = :id
                ";
            }

            $query = $conn->prepare($sql);
            if ($this->id != 0)
                 $query->bindValue(":id", $this->id, PDO::PARAM_INT);
            $query->bindValue(":idFormaPagamento", $this->formaPagamento->getId(), PDO::PARAM_INT);
            $query->bindValue(":idFornecedor", $this->fornecedor->getId(), PDO::PARAM_INT);
            $query->execute();

            if ($this->id == 0)
                $this->id = $conn->lastInsertId();

            foreach($this->transacoes as $transacao){
                $transacao->setIdPedidoCompra($this->id);
                $transacao->salvar();
            }

            foreach($this->itens as $item){
                $item->setIdPedido($this->id);
                $item->salvar();
            }

            $conn->commit();
        } catch (Exception $e){
            if ($conn != null)
                $conn->rollBack();
            throw $e;
        }
    }
?>

The Singleton pattern prevents me from creating multiple instances of an object, but if two people are connected simultaneously, will the same instance be used for the two connections?

  

My concern is that I give rollBack to scripts do    usuario1 and it also affects scripts of usuario2 .

The Doubt