Meed help curving some edges

So I have a school project in which I’m making a 3D model of a cell in blender, and for the mitochondria, I can’t seem to get this shape right. all I need is the inner membrane or the curvy part in the middle. How would I go about doing this, I have tried taking a plane and creating new faces, but it comes out very ridged and looks nothing like the picture.


attatchment invalid. please submit the image as a link for further support.