How will a B in AP Calc impact pursuing engineering/CS?

Considering the list of colleges in your thread Chance a nervous junior for CS , any grade lower than A could add a demerit to your application. One grade lower than A by itself may not sink your application to those colleges, but the more demerits an admission reader sees, the worse your chances will be.

Of course, if you broaden your college search to include colleges are not so difficult to get into, you can relax more.