I checked out an ebook but didn't download at all because realized it wasn't an mp3 overdrive how do I remove it from my #of book chk
You will most likely have to go ahead and download the wrong book and then check it in early, which is actually pretty easy.
Just exactly how you do this depends on how you have your account set up on your computer or device. If you usually use your PC to download, make sure you also have Adobe Digital Editions installed. A quick overview of the process can be found on Overdrive's website, which you should be familiar with from your mp3s. The only difference is using Digital Editions to see what you have.
Then, depending on where you downloaded it (your PC or a reader, or a mobile device like a phone or tablet) you should be able to use either Adobe Digital Editions (on a PC) or Overdrive (on your mobile device) to check the eBook in early, and delete it from both your computer or device as well as your digital account on the library's website. Here is a list of how to return items through both Adobe Digital Editions and Overdrive on various devices.
That should fix your problem and clear up space on your account. Let me know if you have any questions or problems - thanks!