AP - Urgent, Pls Help!

I received an email notice stating my AP was approved and the document was mailed out on May 9th. As of today,May 15th, I haven't received it in the mail yet. Is it normal? I purchased airplane ticket to departure on May 18th. Can I leave the US even if I don't have the AP on hand and ask my family to send it to me later because the case was approved before I leave and CIS won't know which date excatly I receive it? I changed my fly once already and don't want to do it again. Please help. Thank you!