You can increase the number of topics in your course.
For this, go to your course, click on the settings icon, click on 'Turn editing on'.
Now, at the end of your course page, on the right hand side, you will get a 'Add topics' option.
You can add any number of topics to your course.
You can add topics from the course page. You need to "turn editing on" and then scroll down to the bottom of the page. You can see "Add topics" there. The max no. of topics is limited to 52 by default.