Can't tell you what to do, for obvious reasons. I don't know if you are already are at university, or you still need to get in...but you just need to figure out exactly what it is you want to accomplish.
It would make more sense to give it your all at whatever U.S. school you go to, in grades, research, extra-curricular, whatever..and then see where you are in 3 years. If you're not a U.S. citizen or green card holder, then I'd rethink my options completely..
But assuming you are, then just do your best at undergrad, talk to your advisors and keep it up. One year at undergrad really isn't giving it your all, at least not in my book.... And everyone will realize that, including ad coms. Most ppl's freshman year grades are sort of crappy, and they know that.. so just keep working at it. Yes, Ivies give you recognition and so many other benefits in terms of a great education, but even top grades at an Ivy won't guarantee you anything.