Will I lose this chance?

On my application says: Applications must be (post marked no later than Thursday July 5, 2007or be received no later than 5:00 pm Friday July 6, 2007). On my envelop it has post marked date on July 4, 2007 but because I wanted to double check the address I brought the envelope home and I forgot to mail it. It still has the date July 4th on the envelope. Should I still send it? Do you think they will accept it? It’s been 3 weeks now. Should I tell them post office returned my letter because of incorrect zip/ postal code but take the envelope to their office to show the post marked.

I’m lost I don’t know what do to. It’s too late I think.