Reverting back to orginal gingerbread rom is very easy... Just flash a gingerbread rom from samfirware.com of your choice using one package option in Odin. See the steps below if you are unsure how/what to do?
Before you begin it is recommended that you backup your data and applications. Your should should have at sufficent charge to complete the process (recommended around 80% charge).
1. Download a gingerbread rom that is for your region/country from Login - www.SamFirmware.com
2. Extract it to a folder (Password = samfirmware.com) and you will get a tar file.
3. Run Odin MultiDownloader v4.38
4. Load Tass.OPS file and Check One package option.
5. Click One Package button (at the bottom) and select the tar file you got after exactracting your download.
Note: Leave other settings as they are (Don't change any other thing)
7. Now Close Kies and put your phone in download mode (Press Volume Down + Home + Power buttons to go to download mode.)
8. Now connect the phone to your computer via USB Cable.
9. When Odin detects your phone it will show the port in which your phone is connected in yellow background (at the top left).
10. If everything is set and ready click start and wait for 6-7 minutes and let the Odin finish the job.
11. When Odin shows PASS and your phone has succesfully rebooted unplug the USB cable and close Odin.
THere you are with your galalxy mini downgraded to gingerbread. Now go to the recovery (press Home + power button) and wipe the data and cache
partition and reboot your phone).