I sent out the wrong items to the wrong people through USPS.. how do I get the postal service to fix this?

Hello! I typically sell items on ebay and today I went to the post office to drop off some items. One was a t-shirt, the other was a $300 Canon camcorder. They were sent out to the wrong addresses! I was doing shipping late at night and must've got them mixed up. One is to CA, the other to FL. I ordered $200 insurance on the camera. Both packages have tracking #s. USPS hasnt posted any tracking info on their websites yet and I dropped the items off this afternoon. It is now 8:30 and the post office is closed. Is there any way I can get a hold of them to cancel transit and possibly switch the addresses for me!? (besides chasing the mail man down the street). Thanks!!I sent out the wrong items to the wrong people through USPS.. how do I get the postal service to fix this?
Your out of luck. When there gone, there gone.

Just let the people that you sent them to know %26amp; hope for the best. ( I bet that's not what you wanted to hear, is it?)