High school horror movie

theres not much i remember about this movie because i was young but i remember a group of high schoolers meet up in the forest or something to celebrate that they are about to turn 18 and a lot of the people that went to that gathering end up being killed off later on. I think there might have been a school pool death scene and at the end the main character is at his house wearing a long sleeve shirt and hes fighting someone with a kitchen knife

Maybe Class of 1984 (1982)?

Is it a kind of monster or ghost story, or is it more a revenge, because anybody was hurt?

It reminds me of my soul to take