I really need help... I don't know what to do...

So that's good. Now he has 说 hi of course 你 will not stop thinking about him that's what happens when 你 have feelings for someone. No need to worry we have all been there so 你 are not alone. As for what to do, see if 你 can say hello first 下一个 time 你 see him 或者 even see if 你 can get into conversation with him. Just wait and see what happens 下一个 time 你 see him. Hope that helps its a long time since I was your age and I have sort of forgotten what its like to be your age.