Do I still got a shot at going to a good college?

Well, I really screwed up my life I guess. Back in middle school a lot of things were happening in my life (or at least at the time seemed so) and so long story short my performance as a student has been steadily going downward. I'm a Sopre and this will be my 2nd semester. I quit all my extra curriculares in middle school and so right now I've got nothing. I got a D last semester, and so my gpa is a 3.15. I've always felt capable of getting A's in all my cles, it's just i always got lazy and never worked hard. Anyway my PSAT score is 184 (i've yet to take the real SAT) and I was wondering if I was succesful this semester and junior year, would I still have a shot at going to a "good" prestigious universities like those in the UC system or Ivy League schools, etc. If so what do I need to do? Or am I screwed unless something miraculous happens, and trying hard wont get me far because of my past? Anyway thanks in advance for all the advice, I appreciate any help.