AITA for refusing to let my girlfriend stay under my umbrella during heavy rain in a date?

I (NB 19) am autistic and one of the things that I simply cannot handle are raindrops. The overstimulation of rain falling on me is one of the very few situations where I feel like my disability actually impairs me in my day-to-day life. Because of that, I very frequently leave the house with a very big umbrella. Even if it’s sunny outside, if there’s even a smidge of a chance that it will rain, I’m bringing my large umbrella (it’s an expensive Golfer umbrella, these are usually the largest ones you can find. It straps to my back like a backpack.). My girlfriend (F 20) often makes fun of me for carrying an umbrella almost half my size (has a 1.20m diameter when opened) even when the sun is shining bright, but I don’t pay her mind. I’d rather be safe and dry than sorry and wet. Raindrops are a big no-no.

Anyway. Few days ago, I was out with my girlfriend and since it was a date and I wanted to look good I decided to not take my wonky giant umbrella but instead a smaller one. As always, sun was shining bright. Not a single cloud in the sky. We hung out for a bit in a shopping mall (and she commented on my need to have an umbrella even on a sunny day and when we’re mostly staying inside). When we were leaving the mall, however, it was raining a lot. A lot a lot. These kinds of situations are why I bring an umbrella with me at all times. The thing is, as soon as I opened my umbrella, she wanted to stay under it too. I usually wouldn’t have a problem if I had my golfer umbrella with me, but sadly, I only had my tiny one. It was barely enough to cover my whole body (I’m 6’3) when I’m alone, so it wouldn’t serve for anything if we were both under it. We would both be completely wet. I explained to her that it only makes sense if only one of us is under it. I argued that I should have it because I’m always the one who makes sure to come prepared and that my autism does not mix well with heavy rain, but she got really upset that I let her stay in the rain when I had an umbrella. She took an uber home and hasn’t texted me back ever since.

AITA?

Edit: I should clarify that she did try to argue that we both fit under the umbrella, but I don’t think we do. As I said, it still feels too small even when I’m by myself.

Edit 2: For everyone commenting that we were at a mall and could have bought an umbrella:

Yeah, you guys are right. Complete L on both of our parts to not think of that. In my defence, rain stresses me and it’s hard to think, but that’s something so simple I’m a bit embarrassed I didn’t think of that even with the sensory overload.

Edit 3: guys I don’t have a car