You have the email sending before the page loads, so before any form is submitted.
Instead of trying to add the form values to the email body, just add the recordset values directly like you have in the hidden form elements.
In order to make the recordset values available to the email body, just add this to the top of the email body page:
Then you can add values to the email body like:
<?php echo($WADABokning_update->getColumnVal("BokningRefnr")); ?>