DS started water babies at 9 months. It was hard going as I'm a 5ft non swimmer and tbh even the most laid back babies don't get along with swimming at times. Some weeks are good, some are just quite frankly utterly crap.
But.
It's worth persevering. It's about building up YOUR confidence in the water just as much as your baby's. At 9 months your baby will feel fragile and it does feel like you are somehow a bad parent some weeks if they are having an off week for whatever reason.
To get the benefit of the lessons you do have to commit to it, and I think you get to see the real benefit of it when your baby is toddling and starting to actively take part in the lessons themselves once they are mobile. Everything up to that point is just about confidence - and again I stress that's YOUR confidence as much as your baby's in water. And it's the confidence your baby has in trusting you too.
DS recently finished the whole course as a four year old. He's utterly fearless in the water now and is on the verge of being able to swim himself. I've really enjoyed the last 2 years. Prior to that it was hit and miss, week on week. I'm gutted it's over. I hope he never has the same fear of water that I had (and still have if I'm out of my depth).
I'm so much more confident in water myself now. I still can't swim but I'm comfortable in the pool with DS and I don't feel anxious about him being in the pool either. He literally gets chucked in constantly and loves it. If I think back to those first lessons and how hard the mere thought of my baby being underwater was, its really strange.
FWIW talk to your teacher about your fears. They will take it slower for you and help you go at your pace to build confidence. Having a good relationship with the teacher was invaluable to me. That does take a little while for the teacher to get to know you. If you think you want to stand in the corner and do the moves for a couple of weeks say so. You don't have to do everything in a lesson and you don't have to 'keep up with everyone else'. You have no idea if everyone else in the class are confident swimmers - in fact I suspect the reason many do the classes is precisely because they aren't. And yes, your baby will scream during lessons, some more than others, because they are a baby. Other times they will be in the right mood and it's worth the shitty week.
I met a good bunch of people during my lessons. They were really supportive. I'm going to miss them a lot too. I hope we do keep in touch.
I know a lot of people do give it up after one or two lessons which I do think is a real shame. I think there is something of an expectation that it's going to be a wonderful magical experience or something and actually it can be hard work and you only get the benefit from persevering with it. It might not ultimately be for you, but do give it a good crack before throwing in the towel first.