You’re using get_field_id in the name attribute of the “limit” field, where you should be using get_field_name. You’re actually using get_field_name for the name attributes of the other two fields.
Try using
name="<?php echo $this->get_field_name( 'wy_rssLimit' ); ?>"
instead of
name="<?php echo $this->get_field_id( 'wy_rssLimit' ); ?>"
That should solve your issue.
The return values of the get_field_id and get_field_name methods are different: get_field_id constructs a unique ID attribute with dashes, whereas get_field_name uses square brackets to construct an array in the request when saving the widget.