That looks about 10x better than the prototype!
It will be fine. Not ideal, but fine.
Stand the gully on a brick, then pack up with tiles, packers or whatever to get just the right height and level. Then put a couple of bricks on top to hold it down.
You need concrete under the gully. For the pipe, 10mm gravel is the norm. You need 100mm cover around the sides and above.
Or all concrete is another option, which probably makes more sense given the small volume. But use some board or polystyrene sheet to keep it away from the rubber joint and clay pipe, otherwise any slight relative movement will crack the end off the clay pipe.