How do I get out of this detention?

so..I feel really stupid. I forgot to get this paper signed, and it wasn't even that important of a paper. and I forged my parents signature, because I would've gotten detention. I should have just taken the detention. but I got caught for forgery, and they told my dad and not my mom. my parents are divorced. now I have lunch detention, and I hav to get the slip signed. I don't want my mom to find out, and my dad would sign it no problem. but my dad lives far away :| what should I do? don't tell me to tell my mom, please. thanks ahead of time.