How to get rid of this shed

Sloping the soil would never be a bad idea, but more important is supporting the perimeter with a proper foundation. Why do you need a slab at all? Assuming you have a reason for using a slab I would normally recommend a "floating slab" setup, but that is probably not feasible because you are placing a pre-built structure there. A floating slab would require the perimeter foundation to extend above grade in order for your floor to be level with grade. Not possible because your walls and floor are already built. An alternative would be one like shown below (dimensions shown could be reduced appropriate to your structure size). It is critical that the soil and gravel below be compacted.

(1) The fan as shown in the photo is upside down. Mounted in this position, the weight of the fan will pull the plate away from the beam. Turn it over so the weight will push the plate against the beam.

(2) The beam will hold the fan but the weight will apply a twisting force to the beam.

To overcome this, you should mount a board vertically from the beam to another anchor point, perhaps the steel beam directly above. Mount the fan on the vertical board, not directly on the beam.

Alternately you may be able to brace the fan mounting with a chain or other tension member between the end of the fan mount arm and the steel beam directly above.

Of course I'm not there so you'll have to identify and calculate the forces yourself.

(3) If you can, use through bolts with fender washers rather than large wood screws.