My story has a happy ending but gives a slightly different perspective.
I never wanted children. For years I said a flat no, not ever. Then I met DH. He really wanted children. We talked, discussed etc and I agreed. By then, while I still didn't actively want children, I had shifted from being totally anti to mostly just a bit indifferent. I quite liked other children and was perfectly happy to have a cuddle with a baby etc, but I also liked handing them back and getting on with things. I thought my own nieces and nephews were adorable.
We needed some fertility treatment but even on this I made it clear to DH that I wasn't going to go beyond fairly basic treatment. Luckily, while it took a while etc etc, it did work and we didn't need to go into any more discussions.
It was a difficult pregnancy. I felt stressed about it a lot and hated being pregnant. I liked watching DS kick though.
I did not feel the immediate rush of love. I felt a massive sense of responsibility and duty. From the day he was born I knew I would ALWAYS prioritise him, always, but the love took longer. Much longer. I suffered from minor PND. I think this was, at least in part, mourning for the life I'd had to give up. Thank god for an NCT teacher who had said, "at some point, probably at 2 am, you will think to yourself, 'WTF have I done?! I don't want this.' It's okay, and normal". Because otherwise I would seriously have worried that I was a monster.
But slowly things got better. DS started to smile and engage with me. He started doing more, and being a bit easier. Sometimes, I'd be playing with him purely out of a sense of obligation and duty but at some point, that became more genuine. And one day I realised I did love him. I adored him.
I think if children were not in your plan, it can be hard when they come. But that yes, you will adjust. You will love them. I was also very clear with Dh that I wasn't ever going to be a SAHM. I wasn't going to be the type who did everything for the kids while he did his own thing. And he, of course, agreed completely.
You will be fine OP. But if it's hard in the beginning, don't beat yourself up about it. It gets better. 