Your stock has shrunk and is now too short. You could slot the screw holes in the the nose cap, as I remember, they go through the stock (someone may correct me) and thread into the barrel. You will also, no matter what, have to slot the holes in the barrel tenons, as the stock will change length because of environmental conditions over time.
Below is a photograph of an unfired, CVA factory made gun (same design, just an earlier version of your gun), with 40 plus years in a humidity controlled environment (Heat/AC plus dehumidifier in the safe). It’s been on my todo list for years to slot the tenons and nose cap so the stock is free to move over time without opening up a gap between the two pieces, but with a gun that’s never been shot it just doesn’t get to the top of the list.
Oh, and if you eliminate the spacer, you will find the grain of both pieces do not match. Best you can hope for is ‘good job hiding the seam, I can hardly see it’.