You are set to start in Sept at a great college, and all you can think about is how to get into Columbia, from which I assume you were rejected?
Please, focus on starting at Wash U. Forget about transferring, for right now. Set yourself up to get the highest possible grades in the field that you’re interested in, plus if there are clubs or organizations that would give you leg up in that field, get involved in those too. This will give you the most options for internships, etc, but also would give you your best chance at transferring in the future, if that is still what you’re determined to do. You’re probably not going to be able to transfer to Columbia, but Fordham might be a possibility, maybe even NYU if you don’t need fin aid. And a master’s degree from Columbia might be in your future, too.