the cancel and return urls are set in the webassist/plugins/shopping_cart/process_transaction.php files.
look for the following lines of code:
<input type="hidden" name="cancel_return" id="cancel_return" value="<?php echo($WAGLOBAL_Root_URL ."pp_cancel.php"); ?>" />
<input type="hidden" name="return" id="return" value="<?php echo($WAGLOBAL_Root_URL ."checkout_success.php"); ?>" />
you can hard code the address here to use:
<input type="hidden" name="cancel_return" id="cancel_return" value="https://therugrack.com/ecommerce /pp_cancel.php"); ?>" />
<input type="hidden" name="return" id="return" value="https://therugrack.com/ecommerce /checkout_success.php"); ?>" />