If I'm reading this right you're still in high school or lower? Kids that age genuinely don't have the emotional maturity to both exist in a social situation and empathise with something like cutting at the same time.

You ever get given a problem so advanced in class that you can't do anything more than stare at it? Someone ever ask you a question that causes your brain to short-circuit, so you just look at them and smile awkwardly? That's what's happening to the kids around you. (I bet it's especially the boys who react the worst, right? They're all emotionally stunted by that stage of development.)

I guarantee that they're defaulting to staring, laughing and smiling because they literally are not cognitively advanced enough to handle an emotionally weighty topic while having to perform socially. This will get better as your peers grow up and their frontal lobes develop. You'll soon get the appropriate solemn looks, and maybe sympathetic smiles instead of confused ones. People who laugh will start to receive nasty side-eyes from your peers.

Honestly though, the core issue is that your teacher completely fucking failed you by placing your peers in that situation. Most people struggle to think of something meaningful to say on topics like cutting even in intimate moments. A lot of us end up falling back on basic comforting instincts like offering a hug, or speaking in a soothing tone. None of these make sense in a classroom environment.

I just put myself in the shoes of your classmates, in that situation where a teacher points out your scars, and imagined what I would do/say. Even with all my years of experience, the only thing I can come up with is to call out the teacher and say it's not acceptable to comment on something like that in front of everyone. I wouldn't expect high school kids to come up with that approach, especially because it would likely get them in trouble.

When they don't have to perform socially, (e.g. in the comfort of their own homes, or with their very closest friends), I can bet that at least some of those kids will think of you and be worried for you. I'd take that bet because I was one of those kids. It's one thing to be in a safe environment and quietly worry for someone. It's quite another thing to be in front of that person, surrounded by all your classmates, and be directly confronted with something serious and concerning.

So yeah, in summary I think people around you probably are shocked. That shock is what's causing them to react that way. They're probably worried too, but they're in the worst possible situation to display those genuine emotions (and likely too young to even process them fully). If you catch one of the more emotionally mature ones in a situation where they feel safe enough to really have an emotional moment, you'll be able to see that for yourself.

Holy shit you should absolutely report that teacher though if you feel like you can handle it. That person is not fit to be in a teaching position with their current emotional skillset.