On Shape - How to change the shape of a loft between layers.

[BF3D]

Hello!

So i am really new to 3D printing and i bought an Ender 3 a couple of weeks ago to stave off the bored of isolation.

Anyway, i am fairly new to using desgin software as well and recently we a knob broke on our cooker and i am trying to desing a replacement. (Screenshot attached)

all i need to do to finish it is loft from circular surace to the rectangular one evenly. At the moment the loft is uneaven and only seems to go up from two corners. I need the loft to even over all 4 corners of the rectangle.

Im confident this is a simple fix but any help would be apprecaited.

Thanks!