Once your application has been submitted you cannot add documents or comments.
Once your application goes under review, a member of the SBA review team may reach out for clarification or additional documentation. Only then can documents be added.
If you did not get a notice to provide more documentation, you do not need to send it in. Sending a message to the inbox staff or calling the call center cannot add documents to your application. Only the reviewer assigned to your application can request additional info.
So if you think you missed something, just sit tight and the reviewer will ask if they need it.