Bradden Inman's winner meant it was the second time Grayson has tasted defeat in nine games since taking over at Deepdale.
He said: "With the amount of possession and chances we have had we have done enough to win the game.
"In this game and our previous two games we have had more chances to win games than some clubs will get all season.
"You would be more concerned if we weren't creating the chances but we are just not ruthless enough or quick enough to react in the 18-yard box.
"You can't fault the players for their work and commitment it's just not taking clear-cut chances but when we do someone is going to be on the end of a right tanking.
"At the end Lee Holmes hits an amazing strike and it sums up our day that it hits the post with the keeper nowhere near it.
"The things I have seen make me realise what we need for next year but it also makes me realise what we can achieve with the group of players we already have."