Exclamation Wiped GS3's OS!

I wiped my Galaxy S3 completely. It was an accident. I didn't realize I has system checked off. Luckily, I was able to enter download mode and root it through Odin. It reboots into recovery after that, but it says "Signature Verification Failed" every time I try to flash the zip from my SD card. What can I do to fix this? Is there a way to get a recovery onto there to make it easier? Can I flash the zip through Odin (I think I'd need a tar.md5 so I'd need help there, too)?
All help is greatly appreciated. Thank you! I hope there is something I can do still!