How to connect end and beginning of a "ring" with a cutout? I am an absolute beginner in blender and failing at a very simple thing. I have a line lying in a plane. I want this line to have an extension in that plane, i.e. I want to make it a two-dimensional object. I do so by increasing the extrude parameter in the section geometry of the menu to 0.1. What I then get is the following:



I now want to connect the end and the beginning of that object, i.e. to close the cutout of it. From other questions I know that I can achieve this by marking the field U in the section Active spline of the menu. The problem is that the shape of the whole object changes in a very undesired way...

How can I perform the aformentioned connection in a way that preserves the shape shown in the first picture, i.e. in a way in which the extension of the the object stays in the plane defined by the original line etc.?

I attached a blend-file of this minimal-example:
Toggling Cyclic on your curve should not (and does not) affect the shape of existing curve, especially since it is poly type. That could only happen if there were any Automatic control points in it.

If it truly is a 2D curve then press the 2D button to ensure it actually is bidimensional.

In your case you will notice it will ruin your geometry because it is not correctly oriented in local space. Enter edit mode, rotate it 90 degrees in the X axis before making it 2D.

You can finally press Alt+C in edit mode to make it Cyclic.