anxiety about having a total fit in front of my family due to learned helplessness

I am having a ton of anxiety over an upcoming wedding in our family. I keep thinking of the conversations I will be having with the new in-laws. Of course, at weddings conversations about family relations and get-to-know-you questions are the usual. This is what creates so much anxiety for me. There were many people in my family that were not treated well by the bride-to-be's family. They laughed at us, made fun of our culture, said racist things to us at parties, put us down in front of others... it has been terrible for decades now. We never brought it up, out of respect for the kids in the family, we wanted them to have a happy life and not hear about our family problems. So there is so much anger and resentment boiling underneath about the past... I am scared it will come out at the wedding. I have been working in therapy for several years on these issues, hoping to move through it, or leave it behind, find forgiveness, find love, or even just get to the point where I am fine to sever ties. Yet here I am, still dealing with the same issue. I have made a lot of progress... set and maintained boundaries, shared my stories from the past as to how we were affected (a little bit of it, not all of it yet). I actually did so much work on it that I am quite fine with leaving it here and just moving on with my life, enjoying the life I have, and not wasting anymore energy on it. There are times where I feel so happy, life is great, and then I will wake up full of anxiety about this upcoming wedding. I then grab my anxious thoughts and feelings and set them aside so I can enjoy the day but there they are at night for me to deal with. I feel helpless and I think that is why I feel anxious.