Will attach screenshot.

How to fix: in file view.php, replace

echo '<div style="width: ' . $presentationWidth + 2 . 'px; margin: 0 auto; border: 1px solid #CCC;">';

with

echo '<div style="width: ' . ($presentationWidth + 2) . 'px; margin: 0 auto; border: 1px solid #CCC;">';