Generally, schools are a public space (unless you’re in private school). You have no right to privacy in public, nor do you have copyright on the photo. You can request they remove it here: https://help.instagram.com/contact/504521742987441?helpref=page_content but there is a good chance they won’t.
Edit: you live in Italy which has a specific law that photos of children cannot be published w/o permission. Just mention that and they’ll likely remove it.
My child's school sends out a clearance form at the start of every year asking for or to withhold consent. If your parent's provided consent, I'm not sure what more you can do about it.
I'd talk to a counselor about it and explain how it makes you feel uncomfortable.
If you're in a public place (in the US and UK at least) you give implicit consent for people to record you, and they do not have to delete those photos on request. But Facebook might delete the photos from Instagram anyway if you contact them to try and get good PR. Not that Facebook has history of caring abouts users' privacy...
You just go about your day and leave it up like a normal person
Good way to be cast out as a social weirdo at school
There's being privacy minded, and then there's being a social outcast. They're really crossing the line here.
For me, it's more about consent, they really just did that, tf?