Hide the notice in PHP

My problem is this. I have the variables $ qr1, $ qr2 and $ qr3, as you can see in the code below, which are only valid when I send the data via post. But I need them to be hidden from the user so they do not think they made a mistake when they entered the page. How can I do this in this code?

<form class="recipiente coluna margem-topo-100" method="post">

  <input type="text" name="code" required />
  <input type="submit" value="Gerar QR Code" />
  <input type="hidden" name="gerar" value="s" />
</form>




  <?php

  if(isset($_POST['gerar'])) {



    require_once "phpqrcode/qrlib.php";

    $valor = $_POST['code'];

    $code = $valor;

    QRcode::png($code, "Imagem_QRCODE_L.png", QR_ECLEVEL_L, 3);
    QRcode::png($code, "Imagem_QRCODE_M.png", QR_ECLEVEL_M, 5);
    QRcode::png($code, "Imagem_QRCODE_H.png", QR_ECLEVEL_H, 10);

    $qr1 = '<img src="Imagem_QRCODE_L.png"/>';
    $qr2 = '<img src="Imagem_QRCODE_M.png"/>';
    $qr3 = '<img src="Imagem_QRCODE_H.png"/>';

  }
  ?>

<section class="texto-centro margem-topo-50">
  <?=$qr1?>
  <?=$qr2?>
  <?=$qr3?>
</section>