I'm not going to remember plans with my mother.
I wonder why. Do you usually honor your plans with your mother?
I've decided that they aren't that important.
It's rude not to remember plans you've made with people. Set a reminder so that you won't forget your plans with your mother.
I don't want to.
Then you should at least inform your mom that plans changed. Don't leave her out on the lurch like this. Doing what you're planning is so rude.