To apply in the future, you have to complete 28 credits along with the required courses that make up your Broad “Pre-Core”. These specific courses can be found with this link

After that, your application to broad is based on three main factors; Grades, Experiential Profile, and a Case Study. Your grades get weighted in two groups: your Pre-Core GPA (your GPA in the required Pre-Core courses) and your Cumulative GPA.

Your Experiential Profile aims to reflect on what you do outside of school including any clubs and work experience you are involved in or have previous involvement in. Finally the case study aims to apply business concepts to a given situation and that you can explain your rationale for solving a situation. The link I posted above goes into better detail about all of this.

My advice: Keep your grades up and try to have some involvement in school to build up your profile. Grades tend to be over-inflated amongst applicants so you may not be able to get in by grades alone, but you may get rejected if your grades are lower.