My sister, Thea (15F) and I (17F) are pretty close. Yesterday we went out into town just us for the first time (have been out by ourselves before but just with friends) for 40 minutes since it's the holidays and we were bored. It was very fun and Thea offered to bring her money out. We only spent £3.50. Anyway, I have enough money but I'm saving up. Today, Thea asked if we could go out after lunch and I said no since I'm saving money. I am actually, but it's also worth noting I'm autistic (super high functioning) so going out drains my energy and I also get anxiety about it for some reason. Same with my money-spending anxiety. She offered to bring her money again but I said that wasn't fair on her, and I just didn't want to go. My mum was confused as to why and said she thought I'd like it, but I just explained. TBH, my whole family is confused. So, AITA?