I don't think you should worry. I would call the ortho who did the surgery and ask. Better yet make an appointment with them and discuss it, perhaps they can show you some exercises to do with your pup or even send him to pt? I really think it wil resolve. My mini had major surgery on leg and hip before she was 1 yrs old too and I thought the same, she did fine...when she was ready! Good luck!
P.s. If he seems to be in pain please don't wait to call or go to vet.
