Melatonin

I have a lot of trouble sleeping at night and started taking a class that requires me to be there from 9 am to 4:30 pm and want to get a good amount of sleep. I have 500 mg of melatonin, but I'm not sure if it's enough or too much. Should I take 1 or would I need 2? I tried to research it but I'm not getting a clear answer. I read something someone wrote that said taking 25 mg is too much, but here I am with 500! Lol. Anyone have experience with it?