Can I get into Oxbridge or an Ivy League?

<p>I'm only in my freshman year of high school but I want to know what it takes to get into Oxford, Cambridge, Harvard or Princeton. What I really want to know is can I get in if I get A's in all my classes but a B+ in just one for one quarter?
As a Freshman (9th grade) I'm taking:
pre-ap chemistry
pre-ap biology
pre-ap world history
pre-ap spanish III
pre-ap english
pre-ap Algebra II/ Trig</p>

<p>Next year I'll be taking AP functions and analytic geometry, AP physics, AP spanish IV, and AP biology. As a Junior (11th grade) I'll be taking BC Calculus. As you can see, I take the hardest classes possible for my grade level and I'm getting A's in all of them. I have a pretty good shot at being valedictorian and I could probably get a pretty high SAT score. I also do robotics, volunteering and play lacrosse. Last year, I even won a national scholarship competition and I get many acedemic honors every year. My concern really is screwing up one quarter by just a little and ending up with a B+ (which is the position I'm in right now with Algebra II/Trig). So I want to know from the experts and those of you who acually go to these prestigous universities. Do I seem like I have potential? How much does my unweighted GPA need to be? What else would I need to get accepted?</p>