Get to know how the IN, OUT and TO points work. They're really important. You can't pinch-in, copy, paste, silence or many other functions without them.
For mixdown, you need to set your OUT point at the end of the song (The IN and TO points don't matter in this case).
You set your OUT point by going to the end of the song, then hold down the SHIFT button and press OUT at the same time. You do this BEFORE going into Pre-master mode.