I just bought a Ryobi Recip saw to remove deck railing. I used it for the first time today, never having used one before. When I turned it on, the blade wobbled from side to side a good bit. Also, I thought these things cut through screws pretty easily, which this did not. Am I doing something wrong? I am not in the marked for an expensive one, as this may be the only time I am going to use it. I just need to know if I am doing something wrong or is it working as expected?