The all-in-one slide copiers or zoom slide copiers that were very common as (usually) T-mount accessories, allowed 1:1 or greater from a 35mm slide onto 35mm film. So with a less than full frame sensor, it is not possible to capture the whole 35mm slide onto the sensor.
The OP's setup is a little different, as he has a bellows and a separate macro lens, which in principle allows more flexibility, But, OP, your current setup has too much extension - the lens looks like it is focused to give about 1:1, and I assume your Fuji has an APS-C sensor. You need a magnification ratio of about 1:1.5 (imaging a 24x36mm slide onto a 16x24mm sensor). I think the lens needs to come closer to the camera. It doesn't look like the bellows will compress much further, though. An extension tube would usually let you focus the macro lens to the 1:1.5 ratio, but then you need to figure out how to get the slide holder part mounted to the lens without the bellows being in the way.
Nikon made a couple of doodads (ES-1 and ES-2) that can screw to the front of a macro lens and hold a slide, which address this problem. I have the older one of these, and it works, but unfortunately I mostly want to copy negatives, not slides, and it's much better at holding slides.