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I am sorry to hear what happened.
Without a doubt, he needs to see a vet for sure. Considering the nature of what happened, and the fact that it is increasing in size over 2 additional days, it should be evaluated. He may still need antibiotics, and most certainly would benefit from a good non-steroidal anti-inflammatory from the vet.
Also, the neosporin may be insufficient to prevent infection, and that is why oral antibiotics may be necessary.
Worth the checkup for sure.
Since you have opted out the other expert helping you, I will attempt to answer. I agree with Dr. Andy's suggestion that a trip to your vet may be worthwhile, especially if this continues to get worse. Often times, when trauma has occurred, the real extent of the injury isn't seen for a couple of days. I get this a lot with burns and falling events. The skin can take some time to respond to the trauma, often with the death of hair follicles and reddening of the skin as inflammatory cells make their way to the site. If this wound is superficial, like you say, and not actually open to the surface you can get away with not having oral antibiotics. Instead of neosporin, I might recommend you purchasing an antibiotic cream from your local store. I can't think of anything you might have to worry about unless there is extensive damage under the skin, including the potential for a concussion or a fractured skull. This is less likely if the area isn't painful to the touch. Often, the worse thing that comes out of this, is that the hair may not completely grow back. If you do not feel your dog is acting differently, then I would suggest continuing to monitor him and go to your vet if the situation changes.
I hope that helps!