if it's just not inlet enough, you'll have to either put on a new tenon and inlet it and when the barrel is all the way down, drill it through the hole that's already in the stock (the better way), or sink the barrel/tenon down, plug the hole in the stock, and carefully locate the proper position to drill a new hole in the wood to meet the hole in the tenon (the harder way) Even with this, I'd put on a new tenon, 'cause there's no way on earth I could ever hit that hole perfectly.
Depending on whether or not your pin hole is in the "right" location now (meaning in line with the others, and in proper position in relation to any fore end moulding you might have), either one of the above could be the proper course of action.