If you've never organized a March before, you might want to plan it further out. March 31st isn't much time to properly promote, make and distribute flyers, posters, partner w other groups, secure speakers, etc. Also if you're going to go the legal route, you'll need a permit from the city. Unless you only plan to March on the sidewalks. Let me know if you have general questions, I've organized marches and demonstrations in a few states.