Stop guessing and talk to her directly. People are not puzzles. Although it is a common first instinct by many people who experience social anxiety, the answer is never "Speculate and worry until the answer presents itself." Go talk to her.
Definitely seems like something a friend would say/do to another friend, so yes, it seems you were friend-zoned. Which doesn't necessarily mean she doesn't like you back. But altogether, it's a good thing she wasn't calling you a bitch in a harsh manner.
Uhm, she might not be ok with your attempt at girlfriend-zoning her, but it's very hard to say based on a word, if you prefer to not invest time in this if she's not going to be your girlfriend, it's better to get over it and ask, so you can leave if she says no.
I agree with @blackholehead that you should ask her directly. She may have added "bitch" either in a flirty way (I call my best friends "bitch" all the time) or because for some reason she was scared to say that she loves you. Good luck with whatever you choose!
The fact that you think you can be "friendzoned" is very telling. I imagine you're one of those people that think girls "only go out with assholes, tch..." You have not stated clearly to the girl that you genuinely actually like them. Saying "I love you" to a best friend will be taken as it should be taken, a friendly gesture and not an indication of "I want a relationship from you".
It's very possible that you have been friend zoned. But on the other hand, I am always calling my husband names like that. It's my way of playfully telling him that I love him and feel comfortable enough to play with him like that