An easy fix is to change line 373 of templates/schedule.template.php to:
<h5 align="center"><?php $link->doLink("javascript: window.open('popCalendar.php?$scheduleid','calendar','width=260,height=300,scrollbars=no,location=no,menubar=no,toolbar=no,resizable=yes'); void(0);", translate('View Monthly Calendar'), '', '', translate('Open up a navigational calendar'))?></h5>
You can mess around with the height attribute until it looks good.