I'm going to tell my parents about fooling around with my step-sister over a will
Why do you need to tell your parents about the will?
I feel like my parents always ask me about it when I don't see them.
They have the right to know about the will, and you shouldn't mess around and not be serious about it. You can tarnish your sister's reputation by telling them wrong things you might have done with the will.
It's fine, I'm not fooling around with the will. I was just thinking about it.
You shouldn't involve your parents if there is nothing really going on. There is no need to cause them concern for no reason.