Please help!

Since this might be your final chance, you should confess. If you continue to hold it, then at some point you will regret not telling him.

That depends on who this 'crush' is. If it's a friend you will most likely see them out of school as well, so if so would you rather take it more slowly?
However if this person is not your friend (or someone you hang out with normally) try and get a little closer to them first, see how they react with you spending time with each other, and then ask them to the movies, or for a drink.
Once you're comfortable in their presence i say go for it. Just tell them you really like them, and hope the feeling is mutual. If not it doesn't matter, ask that you remain friends instead, that way his/her feelings may grow on you perhaps?
It's entirely your decision, if you feel that your chance will be missed if you don't do it now, then do so. If you feel you will continue to see them away from school etc and you feel like you have some time, get the words in your head straight first.
Either way i wish you luck :)

If in the future you would be able to see him then I would tell him if not I would let it slide.

ok well if u dont want to have sad what if then do it. If u really like them all u can do is give it a shot. fallow ur heart not ur head. if they say no atleast u tryd and wont say what if i did ask? we onley get one shot at things most of the time now is urs r u gonna take it or leave it. now onley u can answer that?