Shhhh you can mail a 13 oz item in a 1 oz and get away with it.
It's called fraud!
Yes, it will usually slip by, as the post office is a mismanaged company that would have been shut years ago if it wasn't government owned.
I once heard a talk show host (possibly Mark L.) that if Apple would say they are releasing a new iPhone. Then change the date. Then say it's really an ipod, back to an iphone. Then screw up on shipping. Ship the wrong color. Mix up the service providers. Then their website would crash, be able to be hacked... the CEO would resign. Possibly suffer law suits, and then the government would shut them down.
However when Obama does the same thing with the New Health Care Reform, no one says boo.
In short, do not worry it will get there.
Also, don't do it again.