If your application really shines, then it's probably not too late. But if you're a middle of the pack applicant, you're putting yourself behind a lot of other middle of the packers. In a system of rolling admissions, that's going to put you at a disadvantage, as you'll be competing with more applicants for fewer spots.
Take an honest assessment of your application. It might be better to take a year and apply early with another year of application-boosters under your belt.