Your grades are your grades - and Bs are fine. Having straight As doesn’t by itself get you into top 20s.
Not having straight As doesn’t eliminate you from top schools.
Unless the reason is unbelievably crazy, you should let it be or it’s excuse making - and yes it shouldn’t come from you.
The world isn’t perfect and you don’t need to be. And if you’re not, roll with it, knowing you’ve done your best instead of figuring out a way to excuse it.
And there’s hundreds of great colleges in this country. Just because US News says it’s top 20 it doesn’t mean it is. And different colleges are strong in different majors.
So relax, be the best you that you can be, and things will work out as they should.