In order to get credit for completing your course/exam, you need to be sure that you view each and every single page in the course. After you finish, you must then click on the "Complete Course" button at the end of the course/exam. Clicking on the "Complete Course" button does nothing if you have skipped pages, so be sure that you have stopped at every page in the course. You can check to see if you have missed any pages by clicking on the "Progress" button in the upper-left corner of each course page.
Give it a try, view all of the missed pages, THEN click on the "Complete Course" button and you should have no problem viewing your certificate.