People often believe that the more complex your topic is, the higher the score you will receive. This is a commonly misconceived notion. In a math IA, they look for how well you can communicate your topic to the audience. While it is impressive to go beyond the syllabus or beyond your subject level, you must also ensure to research and communicate the topic well.
For that, you must have thorough knowledge in the topic, a focused research question, strong math skills and no errors. Pick a topic you genuinely enjoy so that the examiner can feel your passion while reading the IA.