Lots and lots going on here, lela.
Firstly, these fears are really quite normal - maybe exaggerated by your illness, but normal. Trust and confidence have a lot to do with the kind of delivery you have - your mw sounds good, you don't have additional risk factors, and most doctors are not at all familiar with hbs.
Secondly - scans are notoriously inaccurate for predicting size. My consultant (who was generally very anti-intervention) was the head of u/s scanning at my hosp, and says it's good at predicting the size of average babies, but pretty rubbish at very big or very small.
Third - if you don't have gestational diabetes, you tend to have the baby the right size for you. I come from a family of big babies - dd was 10lb 11oz, and ds felt like a right tiddler after her, at 9lb 1oz. I had a few stitches with dd - didn't even notice a tear at the time, and barely a scratch with ds.
fwiw, I was born at home (in the 1970s!) - I was 10lb, and no problem at all. And my mum is very little!
Big babies can be easier to deliver, as you've more gravity on your side. They are also generally quite robust and so, so cuddly!
Late scan photos are just weird, and always look like aliens, even more so than the 20 week ones. The end result is very different!
Now - about you! We say you're strong because you are. Strength and bravery aren't about not feeling fear - far from it. they are about feeling bloody terrified and just hanging on - finding the strength to just get through the next hour.
Remember, by reading these posts again, that much of what you are feeling now is because you've dropped your medication, and so your brain chemistry is not where it should be right now. You've done this, despite the fact that it causes you so much pain, because your instinct to protect this baby is tremendously strong. And that is all he needs right now. He doesn't need you to gush with love for him, to have a sudden amazing bond. He needs you to protect him, just as you have been doing, by keeping yourself well enough to see through the pregnancy.
I know you want your DP to have this "surprise", but honestly, it's like you're worried he'll see the wrapping paper on a present, so you're frantically hiding it in a cupboard. It's just the extra - it's nothing, really, and it is NOT worth this pain. Your DP loves you - your happiness is what motivates him, so don't deny him a chance to help you. Letting him in matters more than any surprise.