I doubt he's stunted, you're just feeding a good bit less than many folks looking to raise them up on the faster side. The fact that he only ate 2 meals between those weigh ins, with the meal before the first being 11 days prior, probably explains the no gain. He could also have been full of crap for the first weigh in and recently relieved for the second. If you want to see faster growth, you can bump him up to larger prey or feed more often - I wouldn't do both since he looks to have excellent body shape, regardless of weight/age.