You say you feel assertive, but I can tell from looking at your body that you don’t feel that way.
Scared, you are trying to override with your mind the honesty that your posture cannot hide. Leading with your chin and rolling your shoulders forward protects your heart. It shows the world you are headstrong. You are not open to new ideas and protect yourself from emotional closeness. Of course you do, that was an adaptive strategy effective earlier in your life.
How we carry our bodies and hold ourselves says a lot about how we feel. Much of the posture we have today is not the result of proper body mechanics and functionally correct alignment. Most of our posture developed as a reaction to the emotional environment we grew up in. That posture becomes our normal way of moving through the world and stays long after the emotional environment changes. Even when our present situation is good, and as adults we are more in charge, our posture often does not change to reflect that. What remains is a protective body stance and learned dysfunctional habits about how to carry ourselves.