It is not necessary for you to do IB to gain admissions to a top university. While the IB does provide a slight upper hand when applying to colleges as the course is deemed rigorous and extensive, you can get into top-ranked universities doing other curriculums as well. However, in order to get into them, you need to be a well-rounded student by taking part in various extracurriculars and cocurricular activities. Another major aspect in your application is the essay. If your college essays show who you are and what you are passionate about, then you might just stand a chance. However, you should keep in mind that quality is greater than quantity as top universities are highly competitive.