TIFU by reading another TIFU and now all the women in my life are laughing at me

Ok, I (23m) love reading this subreddit. I read them all the time in my pass time. I was reading this particular one yesterday: https://www.reddit.com/r/tifu/comments/w8jsod/tifu_by_accidentally_ripping_out_my_iud_during/?utm_medium=android_app&utm_source=share

Now, some background information. I am the youngest in my family. There is a 7 year gap between my other brother, and then 2 more year to my older sister. My parents are very conservative and didn't teach me a lot about sex education. They just let the public school system teach me.

I have been in a very amazing relationship a little over a year now. She (22f) is the best thing to ever happen to me. I have also grown amazingly close to my cousin (22f) over the past 2 years. Both my girlfriend and cousin are my closest friends I have. I feel comfortable talking to them about anything at all, including women's anatomy.

Back to the story at hand, I'm talking to my cousin on the phone yesterday while I read the before mentioned TIFU post. I know that she has had experience with getting an IUD in before. So I told her about it. She then tell me how it is painful to get it put in, she can't even imagine how it would feel getting it ripped out. She then explains the process of getting it out in. Now she says "You know the cervix? It stick it through there, which is painful because of how small it is?" Now, this gets the gears turning in my head. "What do you mean it's super small?" I ask. She says "Well, it's smaller than the width of nail on my pinkey finger." que question marks coming out of my head

My entire life, for a lack of better description, I had no idea that the vagina was a big area that lead up into the uterus through the cervix. I thought that when you had sex, you were sticking your penis into the uterus through the vagina/cervix. I though that the vagina was the "Outside portion" and the cervix was connected to the vagina, like a door and a doorway.

So, my cousin told my girlfriend. My girlfriend told her mom (we are pretty serious, so probably my future mother-in-law.) My cousin also told her mom, aka my Aunt. So now, all the girls in my life are laughing so so hard at me because I had no idea how this all works

TL;DR: I didn't know that the vagina was a large opening. I thought you had sex inside the uterus. I found out by asking my really close cousin who told my girlfriend and then it spread to a bunch of girls I know.