NTA *BUT* lacking sensitivity, perhaps. Best thing about getting older is knowing when to walk away, as the The Gambler song goes, and knowing when to run.

Your speech was fine and could have stopped at “… this doesn’t mean you can act this way towards me.” That would be the kindest place to cut it off. And run.

But who ever gets the words right when someone is lashing out in fear/anger/frustration at them? It’s something one learns. I feel for your sister. It is a really painful spot to be in. As long as she doesn’t continue to pressure or act out at you, you’re definitely NTA for refusing and NTA for what you said because you’re still figuring out emotional dynamics in life. As far as emotional dynamics go, this one’s a doozie.