Why is it that we are always thinking of a vet on a Sunday? Never fails, does it? Murphy's Law, I guess, LOL!
I had this lump explained to me and when the needle goes in, it separates the fibers of the skin and in the healing process, a lump will form, but its not serious and it will dissapate, though slowly.
The odds of a good needle given, I figure are poor at best. Given the tough hide of the cow and having to jab them to get the needle through, then add the cow not standing still for it and if you get a good shot that doesn't raise its ugly head on you, then you are lucky.
I had a horse once that had her shots and all was good until she got silly in the round pen 2 weeks later and tied up on me. She fared through that o.k., but immediately the old needle site swelled up right before my eyes to the size of a grapefruit! Took 3 months to come back down. Vet still hasn't been able to explain that one and I've asked several!
But don't worry about your calf's neck, it will slowly straighten itself out and he'll be no worse for wear.