Enthusiasm is absolutely the most important thing.  After that, self-confidence is the most important thing.  Even if you don't feel like the confidence you need to muster is warranted, you need to muster it.  Wilful self-conviction is one method.  There is a saying, "Confidence is free."  It's true... it costs nothing, but it is a psychological process to enable you to get it for free.  If you are a juggernaut of enthusiasm and confidence, with great ideas to boot, and those kinds of grades, there is no reason whatsoever you can't get into Yale.  The Ivy League is overrated.  I know, I went to Dartmouth ;-)  If you are into the west coast you might also consider Stanford... a great many very successful internet entrepreneurs arising out of there...