Yesterday my grandma picked me up from work at midnight, something that I have never asked her to do, I have no problem taking the bus home, but she insists it's dangerous at night.
I was supposed to leave at 11 PM but I had to stay a little longer. I explained to her that my boss is not an understanding person and that I can't leave when I please.

So when I get off my shift she looks at me and complains about two new acne spots. Mind that I'm taking meds for the acne and it's a lot less worse than it was years ago.

I work at a fast food as a cashier, she told me that I couldn't have acne as I worked with ingredients, I got enraged by this as I don't even touch the food and there is a girl in the kitchen with acne worse than mine. Plus, I was really tired and stressed.

I got angry and said to her in an angry tone that I didn't need her to tell me something that I already knew.

When I told her that she started screaming that I was ungrateful and that she was trying to care for me. Then she started to accuse me of things that had nothing to do with her and told me that I was rude and I didn't care for her at all.

I tried to calm her but then we got into the car and she turned on the music really high so she couldn't hear me.

Was I an asshole? I'm so confused

I'm not an native English speaker, so if you didn't understand something tell me and I'll explain it in other way.