I agree with everyone that you probably shouldn't stress too much about the credentials. Agents like them, but they LOVE well-written manuscripts way more.
Let your words speak for themselves, and don't forget that you can highlight other things besides writing credentials if you have them. (i.e., You've just written a medical thriller, and you happen to be a doctor; your story takes place in Vietnam, and you backpacked through there for three months, etc.)
Best of luck to you!