I think by the time you make a lofted process, please you try use lofted-bend command . The only permitted to sketch is located on the planar surface, not for 3D sketch. And also the end of the plate stretched out must be a flat surface. Even if your drawing can stretched out, so the end result of your plate can't be a flat surface.
You can create a lofted bend feature using Sketch2 and 3DSketch1. It is not true that you can't use a 3D sketch for a lofted bend feature. You can't use your 3D sketch, but you can fix it so it works. Just edit the 3D sketch, right click on one of the sketch elements and select chain, then use the Fit Spline tool in the Spline Tools menu. Don't use any guide curves in the lofted bend, because you can't, and it doesn't need them for what you're doing. The result flattens out.
By the way, stop using the Fixed constraint for everything, it's not helping you out.
I used fix only for this example
This was created in assy and all sketches was "stolen" I broked refs just for this
I try to create part the way Y described