What are my chances and what do I have to do to transfer into an Ivy League?

Right now, i’m a freshman studying computer science at the College of Staten Island, a CUNY. I’m wondering what it would take to transfer into an ivy. My SAT score is pretty average (New): 1200, my high school GPA was a 3.5, I took 3 APs getting 3s on them, but I was still in the top 10% of my class. Additionally, one person got into an ivy (Columbia) who graduated with me. Would retaking my SAT make a difference? Other things: I was on track for a year, and varsity tennis for 3, participated in some clubs, planning to continue working at Chipotle (it’ll be a year in May), but didn’t do much volunteering though…
Currently, my GPA in college is around a 3.8 and i’m taking 18 credits. I took a heck load of credits in high school too, so in total i’m going to have 38 at the end of this semester. Would an ivy even look at my high school stuff? I also don’t know if this counts, but my grandfather studied at Columbia for his Master’s… would they consider that a legacy?
I know there’s definitely more I could do to make myself look better, so should I join some leadership clubs or a sports team at my college? What else is there?