Will a B my Junior Year hurt my chances?

I’m currently a rising senior (will graduate in 2021), and I got a B this past semester in AP Calculus BC. (It’s not a B+, either; just a B.) I intend to major in English and Political Science during college (most of my extracurriculars and activities are English/Poly-Sci oriented), and I got a 5 on the AP test for Calculus BC.
I’m trying to determine how much of an impact this B will have on my chances at gaining admission this school year (I’m currently hoping to gain admission into Tufts, Emory, and BU, with reach schools of Yale and Stanford). I’ve gotten straight As other than the above B, and my extracurriculars aren’t terrible (I’ve gotten some national/international recognition, but haven’t started a nonprofit org or anything), but I know that seeing a dip in the grades junior year, especially in a core class, isn’t great in the eyes of AOs. Any insight on how much of an impact this B will have on my chances would be great; thanks so much in advance.

Relax. If you don’t get in, it won’t be because of one B. Especially not one in what is considered a very rigorous class. You’re fine. ?

You’re more than fine, especially with the 5 on the BC exam as a junior. And hopefully you have a realistic sense of the likelihood of Yale or Stanford anyway – plenty of straight-A students are rejected every year. It’s a long shot for everyone, even an extraordinary student like you.

Approximately the limit of 4x^3 as x approaches zero(+).

Your chances of getting in are probably similar to other students - low to mid single digit percentages, and one B probably won’t change those probabilities out to a couple decimal points.