If he is finished, I would give him 2 scoops (6 pounds) of beat pulp, Bermuda hay and a protein and fat supplement twice a day. I would also walk him for about a mile a day. (This is as long as he is sound).
If he is not finished it would be hard to get finish on him on beat pulp and hay.
The best thing is to get a calf that should finish out about the time of your fair, I would look at a late March, April even early May for a September fair. (depends on calf and it breeding) Our show was in late June we would look at the Late January, February calves for our fair. It is still a crapshoot , some calves gain faster some slower, and some just grow like weeds, but rule of thumb is around 18 months they should be finished.