Recovery is Not Seandroid Enforcing

I have a Sprint S6 Edge. I recently used CF Auto-Root and TWRP, but I must have done something wrong (probably the wrong version) because now I'm stuck on the boot screen with the red message "Recovery is Not Seandroid Enforcing." The volume up-home-power combination to take into recovery mode does nothing, only the volume down-home-power combination works, taking me to the download mode. I have tried flashing my stock rom in download mode but it says failed. The same screen comes up when I restart from download mode. I've looked around and I think it's called a Recovery is Not Seandroid Enforcing Bootloop, but I couldn't find a solution that worked for it. Do you have any suggestions?

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