I'm screwing up in school so bad that I really have no chance of a future.
That sounds difficult. Why do you think you have no future though?
I've been doing pretty badly in all subjects since I started school.
I'm sorry you feel that way about yourself. Everyone struggles in school at certain points though. Try cultivating a more positive impression of yourself and you'd be surprised how your perspective can change!
Well I'm going to fail anyway so why not say what I believe.
Have you tried studying harder? The only way to increase your grades is by studying harder. Once you start doing that and passing your classes you might have a different outlook on the future.