I had a very similar issue some time ago. Check out my thread at http://forum.xda-developers.com/show....php?t=2607252
I went in a few circles, soft bricked my phone, but was able to recover. I think the important thing is to verify if your bootloader has been locked or not; boot into odin/recovery mode and checkout the messages posted in my thread. If the bootloader is not locked yet then you have options. If it is locked, you should probably just reboot the phone and let it do it's thing as the locked bootloader cannot be reverted.
Depends on how important this is to you. My wife got the 4.3 update and loves it, but she is not the type to do any customization. I now have a CM 10 d2vzw and am happy. It I were to do this again, I would probably verify you have an unlocked bootloader and re-flash the complete stock 4.1.2 image as I did. Issue is, you will probably lose a lot of data & settings, but things like pictures, etc. should sitll be there. Once the stock 4.1.2 is there you will want to root and disable updates, or else flash a new rom.