This concerns me, and largely guides my response. This is a huge number of B’s for Stanford (or Harvard, Yale, Princeton, MIT, Caltech, UC Berkeley, …). Also, having these B’s in STEM classes is unfortunate for someone applying for any form of STEM major.
This is the main reason that I think that you have any chance at all at Stanford.
However, Stanford is a LOT of work. Classes go fast. There is a lot of homework. With the quarter system the end of the quarter and associated final exams are going to come up more rapidly than you might expect, and you better be ready.
I still fondly recall when I was a graduate student at Stanford (master’s degree) spending six hours on a Saturday (late morning through about 5pm) working on one single homework problem, out of six problems on one homework assignment, out of five classes that I was taking at the time. Then I went out to dinner with my girlfriend. Suppose that you similarly spend six hours on a Saturday doing one really tough homework problem, and let’s suppose that you are able to solve it. Would you feel that you just wasted six hours on a sunny Saturday afternoon? Alternately would you be excited that you were able to solve the problem?
And I spent lots of time in other cases on Saturdays and Sundays doing homework. This is part of attending any highly ranked university. You need to want to do it.
And how does this fit into a schedule that also includes competing in whatever sport or game you are good at?
How did you get so many B’s? Given that you did, do you want to be a student at a university that is a LOT tougher than high school with significantly larger amounts of homework and significantly tougher exams?