AITA for not sending my girlfriend a happy birthday message

I am currently on a trip in Europe and my girlfriend is out of town with family. Her birthday is today and despite the 10 hour time difference between the Midwest and Northern Europe we were both awake and texting. We were in the middle of talking and I asked if it was midnight there yet, because that would mean that it was now her birthday. She said yes and I sent a big happy birthday I love you so much in all caps with lots of emojis, I then said how much I missed her and wished I could see her. I didn’t send her a prolonged message however just because we were in the middle of talking and I didn’t think to stop the conversation and write a message as if we hadn’t already been mid conversation, although if we were not in the middle of talking I would have wrote a longer message for her to wake up to. Everything was fine and we kept talking until I had to go to breakfast. When I got back I got a text saying that I was being weird and when I asked why, she mentioned how much it bothered her that I didn’t send her a prolonged message, and how her friends did. When I said I was sorry and didn’t realize how much a specific message meant to her and how I just didn’t think to because we were in the middle of talking, she said I was ruining her birthday and how she was incredibly sad. I told her that I was sorry but despite my apologies she kept holding on to the fact that I was making her extremely sad and I currently don’t know if I am the asshole in this situation.

Edit: we are both teens and this has been an ongoing problem in our relationship, she has always felt at a disadvantage or something because she liked me first and for longer, and I am always unintentionally hurting her feelings and making her feel unwanted. I am a very busy person and go to school for music therefore I am constantly dividing my time between friends, family, alone time, and maintaining skill on an instrument. This has been something we constantly argue about and struggle with and I always don’t know whether I am the one doing something wrong. I feel stuck and don’t know if I am the one who isn’t attentive enough.