In the create render node dialog where you select the ramp, there used to be a set of radio buttons with Normal, 2D projection, and 2D stencil. I guess they got rid of it in newer versions because 99% of the time people wanted Normal, which I'm quite sure is already selected for you. If you want to double check you can open the hypergraph, and choose Create > 2D Textures, and at the bottom you can see the radio buttons. If necessary, you'd have to change the radio button before you created the node.