You are missing the brackets.... you have:
<?php
if (isset($_SESSION["eCartCheckoutForm_shipping_State"]) && $_SESSION["eCartCheckoutForm_shipping_State"] == "ON")
?>
13% HST [HST NUMBER]
<?php
?>
and it should be:
<?php
if (isset($_SESSION["eCartCheckoutForm_shipping_State"]) && $_SESSION["eCartCheckoutForm_shipping_State"] == "ON") {
?>
13% HST [HST NUMBER]
<?php
}
?>