Hi Gunter, well the corners are round because all the curve corners are round, the generated surface will follow the same shape as the curves.

If you want to make it become sharp as it goes upwards, try making a sharp cornered profile curve for the top curve, like this:





It would also be good to configure the bottom curve so that it's made up of 3 segments that align with the segments of the sharp curve, see attached 3DM file.

- Michael