How to fix deck board at edge not lined up with beam?
.  Put the last boards down but don’t use the universal clip on the rim joist side. screw the side toward the rim joist but do it at an angle and bury the screw inside the groove  So that the board looks normal and is securely attached (the screw will be hidden).  Secure a board the length of the underlap (or whatever you want to call it) next to the last board so it looks normal.  Get underneath the board and snap a line right next to the rim joist.  Take the board off and rip it for the final piece.  Screw it down from the top knowing it will get covered by whatever railing system I use.  I think that will work just fine and I don’t have to add material.