Lost $475 security dep because I couldn't find a co-signer. Didn't sign anything, is this legit?

I applied for an apartment and put $475 down. A week later the lease was mailed to me and I realized I needed a co-signer. I couldn't get one so I let them know that same day. They're telling me they're keeping my money because the deposit is "forfeit". I can't believe that's possible since I never read anything that said that - am I really out $475?