Try a 45 pound bow. You would be surprised how much difference there is. If that works without shaking, shoot that one for a while. I don't know that I would sell the 55 just yet. If the 45 works, warm-up with that one, then try a few shots with the 55. Don't overdo it, stay under ten shots, less would be better. You may find that you shoot the 55 pretty well.
When I am practicing, I always warm-up with a lighter bow, usually my 45, then work up to the 55. I find I shoot much better with all of them when I do this. Make no mistake, a 55 pound bow is pretty stout. As longbowguy said, mastering it takes some doing. Work on the form with the lighter bow.
If the 45 pound bow is too heavy, the take longbowguy's advice and work up from target weight to hunting weight bows. My 45 pound bow would kill anything I am likely to shoot, but the same arrows sure do get there faster out of my 55!
Hope this helps.