I’m a senior.
I enrolled in AP Calculus BC this year even though my Pre-Calculus teacher recommended me for Calculus AB. However, after the first three assessments, I have a 73.6 in the class. I’m really considering switching into AP Calculus AB so that my grades do not suffer as much.
since they’re both AP classes, I don’t think it will look that bad, and it’s also still earlier in the year. I had the choice between going to BC or taking AB at the end of my junior year, and i picked AB, and I really don’t regret it right now. yeah its kinda hard, but it’s more my level.
If I were in your position, I would most definitely drop down to AB; you’re still taking an AP class regardless, so I don’t think that colleges will hold it against you so much if you were to switch your AP class.
If you’re struggling with a class and there is an alternative that will benefit you, I’d say take that alternative.
Well try your best to bring your grade up and understand the concept before your consider switching, perhaps just get a tutor to help you. 
@MysticKiller74 I just made my decision to switch out to Calculus AB. Hopefully, I’ll have a much better time in Calc AB, but thanks for the advice!
You made the right choice. Good luck.