Fiancé Ex boyfriend is still in her mind

Hi Sir/Madam, I recently got engaged to someone through an arrange setup. We talked for around 4-5 months before we made the decision and I knew she had a relationship in the past. Post our engagement, we decided to get physically intimate and booked a hotel room. While we were making love, she went very low after a moment and seemed just in a different thought being zoned out. I kept asking her what happened and if I did something wrong but she kept saying that nothing happened. I started getting angry and irritated and asked her to tell me the truth or I will leave the room. She told me to let it go because she felt it will affect our relationship. However, I kept forcing her and eventually she opened up. She told me that she was a different body type before. A broad guy with big chest, biceps and six pack abs and I was very different to that body type. While I listened her very patiently at that moment and we made love post that. I'm not liking it now and its giving me anxiety.