Váš dotaz
$select = "INSERT INTO registro (nome, usuario, email, senha, cpf, rg)
VALUES (:nome, :usuario, email, :senha, :cpf, :rg)";
Po změně Chybí:v e-mailu
$select = "INSERT INTO registro (nome, usuario, email, senha, cpf, rg)
VALUES (:nome, :usuario, :email, :senha, :cpf, :rg)";