Change:
<div class="col-12 col-lg-9">
to:
<div class="col-12 <?php if($helper->get('data.event-day', $i)) echo 'col-lg-9' ;?>">
The above is to accomodate when event day is blank to make sure both col-lg-3 and col-lg-9 be displayed accordingly.
<?php if($helper->get('data.event-day', $i)) : ?>
<div class="col-12 col-lg-3 mb-2 mb-1">
</div>
<?php endif ;?>