I tested the "lock" feature on Android Device Manger, and now I can't unlock it I was just testing out Android Device Manager and I tested the lock feature. I entered a password, as requested, and the phone was locked. I was told that since I already had a lock screen on my phone, the password wouldn't be needed. I went back to Android Device Manager and there is only a "lock" option, not an "unlock" option.

Now I can't access my phone since it won't allow me to enter the password on the phone, or unlock it from Android Device Manager.
you have not mentioned which phone you are using, but i found this step in XDA forum, and this seems to have solved it. Could you check if one of the solution helps you: xda-adm-unlock, check out the post #3 by maysider.
Here is the complete snip of the sollution from XDA:


  so the BUG is "made by Samsung". Samsung just do not accept any
  correct PIN or password (maybe because of "wrong" keyboard).
  could anyone tell me how to remove the lock without wipe? thx
  
  edit:
  
  solution 1) just if you have debugging mode on then follow this
  solution http://maxoberberger.net/blog/2013/08/unlock-android-device-using-adb/
  
  solution 2) just if you can change your keyboard for another (if you
  are allowed when entering password)
  
  solution 3) just if you have Samsung account, log into Samsung Dive >>
  "unlock" (my case)
  
  solution 4) no debuging mode + no keyboard solution + no samsung
  account? >> just and only wipe through recovery or Google Device
  Manager
  
  Happy now, but I was lucky
  
  SAMSUNG BUG in 100 %


HTH.

Edit by Izzy: The link with "solution 1" proposes changes made with ADB, which require root access:

adb shell
cd /data/data/com.android.providers.settings/databases
sqlite3 settings.db
update system set value=0 where name='lock_pattern_autolock';
update secure set value=0 where name='lock_pattern_autolock';
update system set value=0 where name='lockscreen.lockedoutpermanently';
update secure set value=0 where name='lockscreen.lockedoutpermanently';
.quit
exit
adb reboot


This will unset your device lock completely, as if you did not have defined any.