AITB to being "rude" to a random person who came into our store after hours?

A random woman came in half an hour after we were closed (door was unlocked because my coworker was about to leave to take out the trash). She asked to use our washroom and basically strolled in through when we were clearly closed (open sign off, mop in use and chairs up).

To preface, I've worked at this store for a year and usually we never have issues with people strolling in as we turn off the front lights, TV's and open sign. Only in the past month or two have we had issues and have had to lock the door, but we're going in and out and so at times have to keep it unlocked.

We had a couple people come in a few days ago being super aggressive and forcibly coming in so I've been pretty upfront considering we're all teenage girls and random older people coming in can seriously be dangerous.

I said "Unfortunately not. Please leave."

The woman (F40 around) started screaming at me shouting that I was being extremely rude and disrespectful and that she was going to report me to my manager and leave a bad review, demanding I apologize since all she did was ask to use the washroom.

Honestly I'm usually a pretty nice person and I felt a little bad for not being overly nice but I had just finished a 12 hour shift and had some bad experiences a couple nights before so I really didn't want to trust a random stranger. It would be a different story if she had bought an item that night, was a regular, or came like 5 minutes after closed, but we we were very evidently closed with the floors freshly mopped and 3 big trash bags ready to be thrown out. Regardless, I knew I wasn't being customer service superbly nice so I apologized and said:

"I'm sorry, but it's just a safety concern."

She continued to shout at me and said thanks for the bare minimum apology but that my behaviour was unacceptable and that she would be writing a bad review when she gets home.

Honestly I can understand her perspective of not being treated with the utmost respect, but it's not like I was like: No, GTFO! I didn't have the most smiley attitude, I just spoke in a monotone projecting tone because people who have come in from the past.

I'm just worried about how to tell my boss if he asks and overthinking me will overthink like always, but was I the buttface?