how active is your snake? - after a meal is it still lively or is a sluggish??
also id like to point out that corn snakes aren't supposed to be chunky fellas, however the backbone should not be visible.

in my opinion - offer your snake another mouse - if he takes it them obviously he may require more food either on a regular basis or every other week, as my snake has escaped before and survived 4 months without a meal it wont hurt it.

What i recommend you do with a snake that is still growing is keep to one size food for about 4-5 weeks, then add the same size mouse(so you feeding it double). after 4-5 weeks increase the size of the food only feeding it one prey item, then again offer 2 of that size. This makes sure that the food item is not too big for the snake to swallow, whilst giving it a chose as to whether it wants to eat more, as my snake does turn down rats if its had its fill.