Looks like you have made the extrusion into a component. First double click the component to open it then click again to select the group box. Now right click mouse and there is an option to soften/smooth edges. I think this is how far you have got. Sliding the bar up and down should remove all the solid lines till you're happy with it.

Are you getting dotted lines on the corner of the extrusion only, or every bend within it? Should be every bend within the shape. Then go to the 'View' tab and deselect hidden geometry. Should be done, fingers crossed.

Shame you made this 2 days to late for me to use, jcb121's was 80x40mm so I resized this using the scale function to make it 45x90mm.