GIMP :: How To Cut Canvas In The Middle

I have an image with many layers. I want to cut a vertical strip out of the middle of one of the layers because I want to narrow the transparent gap between the left side of that layer and the right side. That is, my image has stuff on the left side and stuff on the right and a gap in the middle through which shows the pattern in the layers below, and I want to narrow that middle gap. I want to do the same thing as cutting a vertical strip down the middle of that top layer with scissors so I can scrunch the sides together, so less of the patterns on the layers behind shows through.

Is there any way to do this? It doesn't work when I simply select the area I want to cut and click "cut" or "clear" - those commands don't get rid of the canvas in that section, just the contents, which are transparent anyway.

I'm trying to avoid resizing the canvas and then laboriously reconstructing the layer with all the finicky alignment issues, because that seems unnecessarily time-consuming, when all I need to do is remove a gap in a blank section. I tried using guides to guillotine the image, but that, too, is turning out to be time-consuming in terms of reassembling the image. I know I must be missing something obvious - how does one simply remove a selection of the canvas (and not of the image itself) with the selection tool?