Don't allow the user to try to save JPG templates.

Right now you're presenting the same saving dialog for the regular save and the template save.

Not only that but in either if you select to save as JPEG you chose to throw an error to the user telling them to use the export function if they want to have a JPEG file.

That is wrong, templates being what they are should always be saved in your file format so no JPG option should be present in the selector already. The regular save dialog shows the same problem, if that's not the intended place to make a JPEG out of a document I'd recommend not having that option there directly.