Hey, in the rendering screen, the second item from the top is called "Render Bounds". If that is set to entire project it automatically adds one second to the end of the recorded data (whatever it is). Click on the last bit of audio and then choose "custom time range" from the drop down in render bounds. Set the end time to the time that shows in Reaper (curser position) above the recorded audio. That should have the end of the track or mixdown to the end of the audio. I hope that is clear.