I'm not quite sure how you are scoring the test, but I'll take a shot. I'm assuming that the test score is based on the total number of questions, regardless of whether the student answered it or not. If so, you probably need to include an answer for the skipped questions. You could do this by attaching an action to the Next button on each page that modifies the question variable to an incorrect value if it is skipped. If you don't want to use one of the incorrect values in the original question, you may have to go back and add "dummy" answers to each question that the student doesn't see. That's a lot of work given the number of questions in your test, but I think it will work.
