UPDATE: According to the website, you can correct information at your interview. But, I realize that doesn't help if it's a missing critical detail which will result in denial without an interview. I would still call and see if you can save your application (more importantly the $100 app fee which is non-refundable).

Once submitted, you cannot edit the application. Threre is a screen which pops up to inform you of this and has you review your information.

You can call and see what can be done, but my recollection is that you will need to start the process from scratch again.