Some, but not all of that gap will close down when the final finishing oil is applied if you make a point of applying several "extra" layers.
I know, my close fitting inlayed things like a sideplate will never fit after the finishing oil has been applied until I go back in and cut away the buildup.
Then, I usually end up applying 12-15 coats of finishing oil to my stocks.
In the meantime, try giving the wood in that area a really good soaking with water.
That will expand the wood a little bit. Probably not enough to fill the gap but in cases like this, every little bit helps.
I know, my close fitting inlayed things like a sideplate will never fit after the finishing oil has been applied until I go back in and cut away the buildup.
Then, I usually end up applying 12-15 coats of finishing oil to my stocks.
In the meantime, try giving the wood in that area a really good soaking with water.
That will expand the wood a little bit. Probably not enough to fill the gap but in cases like this, every little bit helps.