I'm still a bit confused. In a way, it seems "Too good to be true". I would craft a nice paragraph and put it at the top of the page so that first-time visitor understands what you're trying to do. You cannot blame people for thinking that this is scam (Hey I'm receiving emails every day telling me I won $1M).
Also, you realize that if I tell my friends about your website I have less chance to win.. why would I do that?
What's your long-term goal with the non-profit?