TIFU by fucking my very real futa girlfriend in the ass ( by accident)

Obligatory this happened 5 years ago but we are still very much happily married today and having lots of sex every day. A bit of a backstory, my dick is fucking huge. I have a 12 inches with 5 inch diameter. I also last really long in bed. Also me and my wife are polyamorous so hmu if you wanna try something ;).

Now, to the story. My wife and I were into vanilla sex only at the time. I was getting kind of bored one day so I suggested she peg me with her giant futa cock instead of the other way around while she masturbates me to vaporeon porn. Now, because my dick is so fucking large, it took a lot of effort to switch positions, and while in the process of doing so, my dominant pelvic thrusts slapped her cock out of the way and it slipped into her asshole. Now, this felt really good, so I kept going even though she yelled at me to stop and that it hurt. After I nutted inside her I sat down on my pewdiepie gamer chair to work on my star wars minecraft build. Reddit, AITA?

TLDR: Accidentaly buttfucked my futa cock girlfiend with my giant penis while she begged me to stop.

Edit: Thank you for the gold kind strangers!!1!11!!

Edit 2: Alot of you wanted a TLDR so I have added one to the end of the post.

Edit 3: Some of you guys are saying I was NTA or am TA for different reasons so I've taken all of your guys'sses' advice and will hit the gym then enlarge my cock then fuck her even harder next time in the dick and make sure to hide the gorilla glue. TYSM fellow holesome 100 fedora tipping keanu chungus redditors.