I'm going to cancel the plans I have with one of my friends but I don't think I want to tell her why.
Did something happen to make you not want to tell her?
I really want to spend some time with my parents instead but my friends tend to think parents are lame.
Not telling your friends something is fine when it's a big deal or really personal but something this small, there's no reason not to be honest. If she asks you should just be honest and if she can't understand that then is she really your friend?
I think you speak the truth here. I will tell her this time and see what her reaction is.
Its good to rethink your plans. I am sure she will be understanding though. Then you can make some plans again and actually go through with them.