If you're not on the latest TWRP, 2.8 or better, you'll regret it.
http://dl.twrp.me/m8/twrp-2.8.6.0-m8.img
If you didn't flash the full SuperSU zip package from TWRP (not the thing where TWRP offers to do it for you) then do so, it's the only way to straighten it out.
You must install the latest version from TWRP -
http://download.chainfire.eu/696/SuperSU/UPDATE-SuperSU-v2.46.zip
If you don't check md5 checksums first before installing anything, you'll regret it (excellent way to brick a phone).
Check out "AFV File Verifier for Android™"
https://play.google.com/store/apps/details?id=sa.afvx
The target values you want are on the download sites for both TWRP and the SuperSU.
To check the TWRP image you need the tool for that, we include it in the Mini-SDK, the sdk-tools.zip file and instructions for use are here. You don't need any special drivers.
http://androidforums.com/threads/adb-guide-updated-2014-11-11.443072/#post-5389081
Unzip the sdk-tools.zip file, it produces the sdk-tools folder - place the TWRP download there.
Windows Explorer, shift+right click the sdk-tools folder, choose open command window here.
In it say -
md5sums twrp-2.8.6.0-m8.img
To copy and paste commands from here -
Alt+space in command window, E for edit - the paste option appears.
The return value you want is -
4970007ee43d536c5e64b56d6b4557b8
Download again if not matching.
On running phone - find and *uninstall* the SuperSU app. Do NOT run it and let it try to install the rest of itself.
Copy the SuperSU zip file to your storage via Windows Explorer. Check the md5 checksum value when done against the one from the download site using AFV.
Power down. Hold volume down while powering on, bootloader appears. If it doesn't say FASTBOOT at the top, tap power as instructed on screen so it enters FASTBOOT mode - plug in to PC, it will say FASTBOOT USB.
In command window -
fastboot flash recovery twrp-2.8.6.0-m8.img
After some bytes transfer and it says OKAY, go to phone.
Choose to go to HBOOT and then RECOVERY.
If you did not make a nandroid backup before attempting root - an absolutely essential step - stop and do so now. The defaults under Backup in TWRP are just fine for this. Optionally, check the box to turn on compression.
When done, Install - navigate to the SuperSU zip and follow the on screen prompts.
Reboot, profit, you're backed up, rooted and you now have the right tools and know how to leave the all in one toolkit behind.
Let me know if you have any questions.