2 to 3 inch groups at 100 yards is 'minute of deer' accuracy
it's sure to break in a bit more, when it does it may just tighten up more.
either way, try firing it with out the fore end on, if the groups tighten up, then an o-ring will help.
i dont see why you cant use an o-ring with the syn. stocks, but i dunno about bedding it.
another thing i do, find a steel washer thats fits over the stud, and grind off two sides so it fits into the oval opening in the stock. this also raises the forend away from the barrel, floating it. you aint going to hurt anything by trying an o-ring or washer, or shooting it without the forend on it..
see what you get group wise, and let us know