So, sorry; I had to leave unexpectedly last night. Ok, so here's what you need to do:
1) Flash Clockwork 2.6.0.1 found here:
http://androidforums.com/evo-4g-all-things-root/259446-clockwork-amon-ra-pc36img-files.html
There are instructions in the thread on how to flash it. If you have trouble with that, let me know. Once it is done, go to recovery from hboot, and you should have clockwork 2.6.0.1.
2) Copy the S-ON tool to the root of your sdcard. You can do so by connecting your phone to your computer as a disk drive and copying it over. Basically, however you copied the PC36IMG.zip in step 1, do that with this file. You can get it here:
http://downloads.unrevoked.com/forever/current/unrevoked-forever-son.zip
3) Go to recovery from hboot, then select the option to install (flash) a zip from the sdcard. Select the s-on tool. Once it is done, reboot back into hboot and verify that it now says s-on.
4) Assuming you get s-on, you now have two choices. Normally at this point, to fully remove root and clean everything up, you should flash a PC36IMG.zip that contains a full RUU to wipe everything and remove root in the ROM. Since unrevoked didn't get that far, it's up to you if you want to flash that and be 100% everything is cleaned up OR just flash the stock recovery back. If you don't even have the Superuser app, flashing the stock recovery should be good enough. Like I said, it's up to you. I'll give you both links.
a)
MEGAUPLOAD - The leading online storage and file delivery service
b)
PC36IMG_Recovery_3.70.651.1.zip
The first one contains a full RUU and will wipe everything on your phone. If you flash that, there will be no doubt that you have unrooted the phone. The second one is the stock recovery. If you flash that, you'll still be fine accepting OTA updates from this point on, but I can only be 98% sure that you're fully unrooted. Since you apparently don't have Superuser or root access in your ROM, it's probably good enough. I'll leave it up to you to decide which one you want to do. They are PC36IMG.zip files, so follow the exact same instructions in the first link where you flashed Clockwork.
Let me know if you have any questions about these steps.