If you record in mono (set the number of channels to “1 (mono)” in the Device Toolbar) then you will be recording both left and right into a mono track, and both will come out in both L/R output channels on playback.
For $10 or $20 USD you can get a pair of cheap (external) computer speakers or headphones. (I assume it’s a cost issue and you don’t want to pay to have your computer repaired?)