I told my girlfriend to play a video game and she got angry because I gave my character a nickname given to me by a friend.

tl;dr I would like to know if I was the one who did something wrong here.

Today, I (m17) proposed to my girlfriend (f17) that we play something. She accepted and we created our respective characters. I didn’t know how to put it at first, and later I planned to change the name again, so I gave myself a nickname given to me by a friend. My girlfriend has an insecurity about her partner changing her for her friends, because her ex did that to her. She was upset by the nickname, saying, “You were supposed to play with me. I thought you’d put yourself in a way that reminded you of me,” and sure enough, that’s what I was going to do. I tried to explain the situation, but with each word he got angrier and angrier, to the point of talking to me in a worse way. I was trying to calm her down, but she wouldn’t listen to me. I thought that, in all this time, I would have shown her that I was not going to change her for anyone, but apparently it was not like that. I would like to know what I did wrong exactly. I understand that she had an insecurity because of her ex-boyfriend, but I did not expect that for a name of a video game she would get so angry, and I want to know if I was the one who ruined everything.