Change the code for outputting the contents of the form:
<?php foreach( $_POST as $pkey => $pval ) { ?>
<?php echo(str_replace("_"," ",$pkey).": ".($pval)); ?>
<?php } ?>
to:
<?php foreach( $_POST as $pkey => $pval ) { ?>
<?php if(is_array($pval)) { ?>
<?php echo(str_replace("_"," ",$pkey).": ".(implode(", ",$pval))); ?>
<?php } else { ?>
<?php echo(str_replace("_"," ",$pkey).": ".($pval)); ?>
<?php } ?>
<?php } ?>