1) It is never helpful to have Bs when applying to HYP, but it happens. In my opinion, 2 isn't that bad, and it's helpful to remember that everything is evaluated in context. If you are rejected - and I hope you aren't! - just know it won't be because you had 2 Bs on your transcript.
2) I didn't plan to major in science or math in college, but I took calculus anyway. Why not pursue a subject to the highest level available to you? Taking the easy route never scored anyone brownie points with an admissions committee.
And personally, now that I changed my mind completely and will be concentrating in a science, I've found that having taken the AP science and math courses I did in high school means that the transition from the humanities was a little easier.