Bummer! You should have uninstalled on the day before the end of the trial. The Uninstaller is also subject to the trial period limitations.
If you plan to buy a full license, you don't have to uninstall the trial version at all.
It's exactly the same binary you'd be getting anyway, and it's the same binary for the Extended and Standard version of Photoshop. It's your serial number ("key") that turns it into either Standard or Extended.
I'll bet that if you attempt to launch your expired trial version, it will prompt you for a valid license number or to buy the license. So when you have bought the license, just input the serial number there and you're good to go.
If you're absolutely itching to delete the trial version, and provided you have no other CS applications (any version or flavor or CS), then just drag the Photoshop folder to the trash, empty the trash can, and then run the Adobe CS Cleaner Tool, which you must locate on the Adobe site and download. The Cleaner Tool will (should) get rid of all the other components scattered by the CS6 installer all over your HD.
Hope that helps—at least to put you at ease.
Enjoy your Mac. Typing "MAC" reveals you are relatively new to the Mac, congratulations!. It's Mac for Macintosh.
For some reason, the Photoshop app and everything related to it doesn't launch since the trial ended. Do you happen to know if I would purchase the full edition, that the app would open and prompt me to enter the serial number?
Thanks for your response!
No. If it doesn't open now, it never will.
The poor thing has no way of knowing you bought a license.