You're not alone. I have had simlar issues with keeping my shoulders relaxed. I work a very stressful job, and I often go to the studio carrying that stress in my shoulders. It can be tough at times to let it all go. Try to relax. I know that is easier said than done, but at least try. Stretch, breath deep and slow to calm yourself. Stand before a mirror. Compress the muscles in your upper back that draw the shoulders down (mostly the latissimus muscles or lats). Look to see how it looks. Feel these muscles with your hands. This should give you an idea of how to use the muscles that function to bring your shoulders down. We have to learn how to do this, so find the way that works the best for you in learning this. Practice using these muscles often, and over time, it should become a part of your "muscle memory." It all gets better with practice over time. I presume you are a lady, so ask other women for advice on this, as well. My teacher is a woman, and I often seek clarification from male coaches particularly when it comes to "body mechanics." There are some very knowledgeable ladies (and men) on this site who should offer up some information on your question.