Again if you closed the session, you can't add anymore files to it, you need to erase it and re-write it, but you need to leave the session open if you want to add more files at a later time.
Your burning software should have an option of this at the time of recording it.
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Ignorance is not necessarily Bliss, case in point:
Unknown has caused an Unknown Error on Unknown and must be shutdown to prevent damage to Unknown.