Did I read it correctly that he is in a food container? That could be part of your problem -you are stunting him. A single larva should be given a minimum of 2 gallons while developing the front arms and then moved into a larger tank as the back legs grow in. By the time it is has fully developed all the back legs it should be in a 10 gallon tank.

At this point you need to do a massive upgrade immediately but I cannot say whether or not the damage is permanent, it depends on how long he has been in this container. Keep up on the foods you are feeding. Other than that, they all grow at their own rates but should grow to be full grown with in a year to a year and a few months, this could be about 6-10 inches depending on their genetic history.