So basically Ive been working with this girl who is a 7. We have been flirting and having playful banter with each other for about three months. Me and my coworkers all went out drinking last weekend and I felt like she was showing interest in me. I was isolated with her and had my arm around for half of the night.

This past week when I came back to work, I continued my playful banter and negs. I accidently said some harsh things and she seemed genuinely pissed. Every time I tried to talk to her she would snap back at me. Normally she would approach me at work to talk or ask me if I need help. But now, I have to approach her to talk and things seem awkward(she's mentioned that Ive been more quiet than normal). I feel hesitant to neg her at this point and dont know what to do.
My question is how do I make things normal again and what should be my next course of action.

no expert but probably because after ur date the attraction is over and it has to switched to comfort, please provide more information, howmuch tiem is this this entire interaction taking place

If you were isolated w/ your arm around her why didn't you close? the point of negging is to disarm so that you can isolate. you were past that point. she probably got pissed because she was giving you all kinds of IOI and you did nothing. now she feels rejected. In her mind she basically threw herself at you and you did nothing with it. To make matters worse you made fun of her at work the next day. That's not negging, that's humiliating. Its past the point of being smooth and to continue would take you from picking her up to dating her. if thats what you want then just apologize and offer to take her out to dinner to make it up to her. but chalk it up as a learning experience, if you're isolated and getting that kind of IOI, its long past time to close.