
If a woman had been credited with discovering gravity, this would probably have been the way, yes it is normal for some of the ejaculate to drain.
I'm going to be very honest here, if you know so little about the canine reproductive process you should not be breeding. The book of the bitch is just a start.
Have both the dog and bitch had the relevant health screening tests, for most breeds that is at least Hip scoring under the KC/BVA scheme, eye testing by a BVA panel ophthalmologist,a nd any other breed specific tests.
How well do you know the ancestors of your bitch and the male, to decide if they are the best mates for each other to produce sound healthy typical puppies?
My advice would be to take the bitch for an Alizin injection at the end of this season, to prevent a pregnancy until you have studied a lot more. Breeding should not be gone into without a lot of thought and knowledge, as you will be responsible for the lives created and possibly endangering your bitch.
Would you consider having a baby with only a friend in attendance who only had the most basic knowledge of how the pregnancy happened.
What you need is an experienced breeder on hand to help you with advice on the care of the bitch and to actually be there at the birth so that you are aware if things are not going as they should.
You canto simply rely on the vet as most unless they breed themselves have little beyond theoretical knowledge of breeding and whelping their expertise is saving the bitch if a C section becomes needed.