I included an options panel in it which is licensed under GNU version 3. Does this mean I am allowed to use it in a WordPress plugin?
Yes it does.
I want my plugin to be listed in the Plugin Directory, so it must follow the guidelines.
That's a good thing. ;) Give these articles a read if you haven't already.
I'm not a plugin reviewer (and that's a good thing too, my PHP is awful) but the guidelines aren't that difficult. If there is a problem with your plugin submission then I believe you'd get an email.