AITB- my girlfriend is overreacting to me jerking off to porn?

AITB- I (19f) had been dating my girlfriend (18f) for 4 months at this point. We were telling each other about our days and I told her about how a familiar porn star came up on my TikTok fyp so I decided to open up pornhub and jerk off to a video of hers. At first my girlfriend thought I was joking, I explained to her I wasn’t and she got very upset. She told me about how insecure and grossed out that made her feel. I feel very bad that I’ve hurt her, but is she overreacting?