You really should hire a lawyer to help you prepare a contract like that, as well as to help you sort through what intellectual property you own and do not own. While you say you just trademarked the logo, you likely do not have any trademark rights in the logo. Trademark rights arise from the use of a trademark, not the design/creation of the mark. The organization therefore likely owns the trademark rights (since it's the one that's been using it), and an application to register the logo in your name with the USPTO (which I'm guessing is what you've done) is probably invalid.
If you created the logo and haven't signed any written agreement regarding copyright ownership, however, then you likely do own the copyright in the logo design. Same thing with the website. But there's also a good chance that a court would find that you gave an "implied license" to the organization to use the logo and website under copyright law, regardless of whether you were promised some kind of compensation or benefit in return.
In short, I'm afraid you've already made a few mistakes legally, and trying to prepare your own contract would just compound things. I know the DC area lawyers are very expensive, so you might want to look in other metro areas of Virginia like Richmond or Roanoke. Just look for someone that practices trademark and copyright law on a regular basis. I'm happy to have a call with you to explain a bit more and help guide you with finding a lawyer in your area.