Unfortunately, superSU really doesn't take you back to stock configuration. It disables root access, but that's all.
Since you posted in the Sprint forum, I'm assuming you have a Sprint phone. If that's not the case, DO NOT FOLLOW this advice.
The best way to unroot a Sprint phone,, I think, is described here:
http://forums.androidcentral.com/sp...-30-2012-sprint-only-unroot-return-stock.html
But in order to run the first part of that procedure, to get rid of the modified status, you need to be rooted. You could follow the steps here:
http://forums.androidcentral.com/sp...e-updated-how-root-your-sprint-galaxy-s3.html bu there might be a simpler way.
IF you still have a custom recovery (CWM or TWRP) try this first, and if it doesn't work you can follow the procedure I linked to, or reroot with whatever method you used before. If you don't have a custom recovery, you'll need to reroot from the beginning:
1. Download the SuperSU flashable zip from here:
UPDATE-SuperSU-v1.65.zip | by upndwn4par for Galaxy S 3 Note the countdown timer on the right. Wait for it to hit zero, then download from any of the mirror sites that appear.
2. Copy that zip file to your phone's memory or SD card. DO NOT unzip the file.
3. Boot into recovery, and install the SuperSU zip, then reboot the phone.
4. Check to see if you've regained root. If so, follow the unroot and return to stock procedure linked above. This will actually return your phone to Android 4.0.x. You'll be notified of 3 OTAs. The first two are Android 4.1.2, the 3rd will be Android 4.3.