I'm sorry OP.
I think you shouldn't talk to him this morning when he's hungover.
Don't wake him up either. Get ready for the scan and go. If he wakes up in time, he comes, if not, he doesn't. He's going to be a father very soon and it's not up to you to teach or mother him into it. Who is teaching you to be a responsible adult/parent-to-be? He needs to take responsibility for himself. It's his responsibility to get himself ready and be present at his baby's scan.
If he misses it then that's sad. But it's not like him being drunk or badly hungover while you're in labour. And you have spoken to him already, he's not listening. You need him to hear you, so don't say one thing with your words and then do other things with your actions. If you don't want to mother him, don't and don't be allowing yourself to be in a position where you feel guilty for not treating him like a teenager!
I'm not blaming you at all btw! I've been there myself. I know many women who have been too. We want to make it good for him them, we want to make sure they're on time for baby's appointments or school plays, parents evenings, birthday parties, dinner etc. The emotional labour is HUGE. But you don't need to sign up for it. You're not being unkind by not either. He's an adult, it's his job to take responsibility for his actions and not have you softening the blow of his actions/inactions.
So don't talk this morning, see if he comes. If there's medical news then call him. If he's angry at you for not waking him up, or says you're excluding him, then don't take it. It's basically DARVO because what he should be doing is apologising to you and being angry at himself for not getting himself up and ready.
Have a think too about a backup plan for if you go into labour and he's very drunk. Would you want him at the hospital with you (you certainly don't need a vomiting drunk there!) or is there someone else who could be with you? Who could drive you there?
Then this afternoon talk about it and don't give big explanations. Be to the point and businesslike. Tell him you'd have gone without him and that from now on he takes 100% of his responsibilities, because you have enough to do without him adding to them. Tell him you're going to ask X to be a backup because you need to know that you're not going to be alone, but you really really hope that he'll be there for you and the baby.
As an aside, if he's drinking that much that often, he's got an alcohol problem and long term you need to make sure you have options for you and the baby if it continues.