First off: sorry I know these posts are obnoxious. 
Second, I am a junior currently taking 5 Weighted classes and 1 unweighted class (English). English has never been my strong point, but I have never gotten anything less than an A until this year. I got a B in english and As in my weighted classes. How does this look to admissions?? I’m freaking out rn!
Also, I will mostly be applying to the UCs fyi
One B will not make or break your admission chances. Relax and continue doing well in the rest of your classes. No one is perfect and even perfect grades are not a guarantee of admission to most of the UC’s except maybe UCM/UCR.