Please persevere with the alloy. You will get there and increase your already great skills. You just need to shrink the area of the flange slightly to remove the excess metal that is causing the ripples. Make micro shrink tucks along the edge and hammer them smooth, take your time and you will get there in the end. It often helps to have a larger flange as you can shrink it more in the edge and still trim at the end to suit. Picking the right metal and temper are key, if needed heat treat at the end to correct hardness.