First... take a deep breath....hold it for five seconds, and let it out....

Now, I'm pretty sure from your description that if he does have a burn, it's probably minor, and putting anything on it may do more harm than good. If I were in your position, I would wait a few days and monitor the appearance of his belly. If it looks any worse during that time, take him to the vet. Until then, just keep an eye on him, keep his temps within the proper limits, and if you can, maybe get a pic of it and post it.