Being married to a developer is awesome. This fix will make the slider auto-centered everywhere. So with this php edit, you will still not have control over changing the alignment should you want the slider left or right aligned.
On you Dashboard go down to Plugins > Editor. Use the top right dropdown box to set “Select plugin to edit:” to TwentyTwenty. Below this dropdown you should see a list of php files. Select “twentytwenty/public/class-twentytwenty.php”.
If you scroll to the very bottom of the file you should see this line of code:
return '<div class="twentytwenty" class="twentytwenty-container" style="display: none; max-width: 100%; width: ' . $width . '; height: ' . $height . '">' . $images_code .
and change that one line to:
return '<div class="twentytwenty" class="twentytwenty-container" style="margin: 0 auto; display: none; max-width: 100%; width: ' . $width . '; height: ' . $height . '">' . $images_code .