Start from scratch.
First inspect the barrel. Is all the rifling in the barrel.
(Bought brand new in the box Rem Model 700 and was missing 6 inches of rifling) Take the bolt out and hold barrel up to light.You did clean the new barrel before shooting? Right?
Next check all the screws on the rifle make sure they are tight. The 2 on the bottom of the stock holding the trigger assembly.
Remove scope and rings. Place target at 25 yards. try your 3 shot group through open sights.
If group ok then rifle is fine.
Now put scope, rings back on and set target at 50 yards.
3 shot group again. If bad, scope/rings may be bad and try different scope/rings on new rifle.