How do I calculate the range of this curved ramp I'm building?

That's the beauty of the energy equations is that it doesn't matter what path you take, just the end points. The only problem is if friction would be a major factor involved. If you think it would be then you would have to integrate along the curve, but this is probably more complicated than the equations need to be. As long as you took the angle and the end height into account you should be fine.