What Matt said. You need to give the command to "Rest" But, you may need to add a new chord in the bar just after where you want your sustain to end and place a dot/period at the end of the chord.
Like this.
/C.../ /C. /
If this is the end of a song and you are not using the BIAB generated 2 bar ending it may help to add/leave a few more blank bars after that last rest then place another rest chord on the very last bar. +
Like this;
/C... / /C. / / / /C. /
I find that some styles behave better this way.

Worst case is; add a few extra bars as described. Convert to .WAV. Open in a DAW, such as Audacity, and edit off the last chord after the few bars of silence.

Does the noise in your head bother me ?