Close, but not quite! Under the AGPL, you only need to make the source code available to the people who interact with the software over a computer network. You don't necessarily need to contribute the code back to the main project.
> 13. Remote Network Interaction; Use with the GNU General Public License.
> Notwithstanding any other provision of this License, if you modify the Program, your modified version must prominently offer all users interacting with it remotely through a computer network (if your version supports such interaction) an opportunity to receive the Corresponding Source of your version by providing access to the Corresponding Source from a network server at no charge, through some standard or customary means of facilitating copying of software.