
Were you too early? I don't necessarily think so. If she's a maiden bitch, it was probably always going to be the case that she'd complain. But on the other hand, if she wasn't ready, I doubt she'd have let him mount and penetrate at all. And he'd probably not have either. If he's an experienced stud dog, he'd not bother if she wasn't right on (usually). Sperm lasts for some time once there in any case, so even if you were a day or two early, she'd still probably conceive.
I had one of mine who vocalised during the mating, and again during the whelping - she was just one of those