Is it okay to have 1 B in my transcript to be qualifable for top 10?
Yes. Relax. But also commit yourself to not making excuses. If you are admitted, it obviously didn't hurt you. If you aren't admitted, it wasn't because of the B+. Holistic admissions means that once you clear the bar academically, which you will, it is about what you do affirmatively with your time to better yourself, your community, etc.