Your rubric should include objective scoring criteria. Your site meets the criteria for a specific score or not. You must apply your rubric and determine the score based on your rubric.
If you think your score should be different that what comes from applying the rubric criteria, that’s fine. But you must also change the rubric so the criteria and ratings match the final score.
This is part of developing the rubric – comparing the score determined by applying the rubric with what you think the score “should” be then adjusting the rubric, criteria and/or rating.
Are you judging the web site on appearance but scoring the mechanics, for example? A really attractive page may not have included all the required elements, or included coding mistakes that didn’t affect the visitor experience. What exactly is is rubric measuring?