You don't need to submit and finalize until you are ready to. There is no save button; Bonfire automatically saves your progress on the fly as you work!
The next to time you login, simply go back to the Project you were submitting to by clicking on the corresponding View Opportunity button.
and scroll to the Submission section near the bottom of the page:
Here you will see your Work-in-Progress submission(s). Click the "Continue Submission" button to resume exactly where you last left off!
Already finalized and submitted and you need to modify your submission?
Keep in mind you can even un-submit a submission all the way up until the close date of a project:
Related terms:can i start the process and come back to it, resuming, begin submission, continue later, do I have to submit all at once, can I start my submission in advance, begin, finish later