Used wrong shipping service to send package. What do I do?

I sold an iPhone on Amazon yesterday, but the buyer didn't buy until after 6pm, so I shipped today.
The problem is… I printed out a shipping label from Amazon while I was in the UPS Store today and everything went fine. I purchased insurance on the phone and everything. I decided to check on the shipping status of the package, just to make sure that the information was in the system and all was going well with it and the tracking number did nothing on the UPS website, it wasn't even recognized. Then, I realized that the shipping label was printed out for USPS, not UPS.

So, I rushed to the USPS website and checked the tracking number there as well… No luck. The tracking number was not found. I realized that I made the mistake in over looking the shipping company, but what do I do now?

I don't think UPS and scan and ship a USPS shipping label.

If the package got into UPS hands, it will eventually be handed over to the USPS. The package should have some sort of tracking that you can see because an Insured Number is not viewable except on a USPS computer.