My boy Tux swelled way more then that, I did take him back but they assured me as long as it wasnt leaking that the swelling would go down and that it was normal. But they also gave me pain meds to keep him comfortable. The swelling never seemed to bother him, but again he was on pain meds.
If your concerned take him back for a quick follow up. My vet does it for free after a surgery until they have fully healed. Not sure if yours does?
Again I wouldn't be overly worried, but I would at least call and ask about it, and inquire about the pain meds.
Also my male dog swelled like that too, more because he was already 5 years old so they can react differently when fixed then a young dog that hasn't fully matured yet. Same for Tux he was already 2 when he was done so I don't know if age can play a factor in the swelling. Iv had young male dogs come back and not swell at all.