I'm not trying to be r/iamverysmart but, I've always been above average with academics, namely math and science. my older sister always disliked that and came up with excuses about why I was ahead of her when I'm a year younger.

When I was in year 10 we tried more difficult math as I wasn't learning and she wanted to get ahead. I moved up two year levels from year 9 to year 11 (level one) and she moved up one year 10 to 11 in math 2 years ago, ahead of her, then she stopped competing over math, and at the end of last year dropped back a year to do calculus, as originally she'd gone into statistics (I was in calculus so we didn't worry about class over lap). All was good until this year I joked about visiting her physics class to confuse the teacher. She didn't know it was a joke, she wasn't listening fully, got really serious and said "**Don't.**" after I told her it was a joke she relaxed a bit and I laughed it off. She said it some more times over the next couple days about not doing physics, at that point I had no intention on doing it.

Right now I'm in 13 calculus (level three) I'm ahead of the year 13's and working on my own thing, my year 12 calculus teacher came up one day said I should move into year 12 physics (level two), I dismissed it because of my sister but wanted to do it. The next day I had my second science lesson, the first one was boring. I found out it would be recap for at least half a term and probably more, I just felt constrained. I thought about moving up to level two physics and possibly level two chemistry. That evening on the way home I casually mentioned moving up in science, my mum was immediately hooked and started sorting out the details with me. Up until this point I hadn't seriously thought about moving up, just some maybes in my mind. My mum sorted out the class changes and I got moved up into the subjects (my mum is a teacher) and it turned out there's only one physics class and one chemistry class so I'm in two of her classes. I attended one physics lesson when my sister was sick and that's all I've had.

Today I went with her to her job interview to calm her a bit she was thankful. When we got home, because I thought she would take it better when she was happy with me, I just out right told her. I didn't want to just show up one day in her class. Now she's furious with me and I don't know what to do. I don't want to make her sad, but I didn't do this to piss her off, so I'm kind of annoyed she got upset. Am I the Asshole?

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TL;DR: My one year older sister really didn't want me to move into her science classes and told me repeatedly not to after I joked about it, but my classes weren't teaching me anything and I felt restrained with learning, so I did. I ended up with her in two classes, she's now furious and I don't know if I'm in the wrong.