Going to keep this short and simple. It's a lot more difficult to transfer into a limited enrollment program after you've completed 1 year of post-secondary education (compared to applying at grade 12). Unless you are sure you are able to get good marks during your first year of studies; good enough to be extremely competitive. I know for a fact that if you plan to transfer, your extra-curricular activities are not considered important anymore, because your MOST recent marks (i.e. your post-secondary education marks) are their main priority - there should be a form that you fill in with a faculty member that lists all your university course marks and, in that form, you won't even see a section for EC activities). At this moment, you should find out which staff member in the faculty is responsible for transfer students and find out about the statistics (ex. roughly how many students apply for transfers and how many students get accepted or what marks they are expecting). Again, just a heads up, you're looking towards a lot of work to be done during your first year if you take this step.
If I were you, I would definitely see what other opportunities are open for you, because other limited enrollment programs that you enrolled into would be just as good as Ivey. Or, if you are really that desperate for Ivey, take an extra year in high school to upgrade your marks even higher, so you can be even more competitive. But transferring or taking an extra high school year does not guarantee you enrollment. Consider the pros and cons of your decisions.
Sorry, I meant to keep this short and simple, but I don't know what happened. All in all, the final decision is in you, so make sure you support your own decision and don't ever look back. Good luck with your decision and future studies.