cis is supposed to mean that your gender identity matches your biological sex (and immediately that means you have 'privilege' over anyone whose doesn't. Enter the whole 'feminists must centre trans women' argument)
So the moment you use the word cis you buy into/ validate the politics there.
It also means you buy into the whole gender stereotypes thing if you feel your 'assigned gender identity' matches your biological sex. (ie if you have a vagina, do you like pink, long hair, high heels, are emotional and irrational, poor at parking and maths/science, please park your stereotypes and disempowerment of women here.)
I don't buy into gender stereotypes. I believe women come in a massive range of shapes, sizes, personalities, likes, dislikes, skills etc without any of those indicating a 'gender'.
So no, the 'assigned gender' associated with women does not to me equal people with vaginas, xx chromosomes and the capacity to gestate a child. I am not 'cis'.
And besides all that, to me its very rude to go around shoving labels on people to force them into boxes of my choice without consulting them first.