mounting a red dot

Brand New here. Brand New Sub 2000 Owner. 9MM Saying Hi All. Mounted a Bushnell TRS 25 Red Dot, Bottom of Bushnell mount is Flat. Sub 2000 1913 Rail is slightly sloped like a gable rooftop slanting/sloping left and right. My TRS 25 rocks and will not lock solid and tips left to right. Shouldn't...