Supplemental asks about intended major but I'm undecided

One of the supplementals asks, “Describe your academic interests and how you plan to pursue them at USC. Please feel free to address your first- and second-choice major selections.” I made my first choice major “Undecided.” How would I go about this essay? Am I at a disadvantage for selecting Undecided? USC says if you don’t get admitted to your first or second choice majors but they still accept you to the school, they mark you for Undecided automatically, Would my chances of getting accepted increase if I just chose a major and if I didn’t get into that major, I’d be considered again for Undecided?