I have never designed my own quilt. I follow patterns but I do change them to suit me. I just made a quilt for my granddaughter and when we were laying the blocks out, my DH and I did not like the wide sashing. He and I agreed it was just too much. So we made it narrower and added a red cornerstone. It turned out beautiful. I tend to do that quite a bit, just tweak something that didn't turn out right. But I always start with a pattern. You are not alone.