Hello Rlash, since you are working with Mono files, the only way you can have them coming through both sides as a Stereo file is by duplicating that mono file. This means, you will have two tracks, each with the same Mono file, this way you can pan them to each side and when you mix the tracks together, you will get the Stereo effect from both tracks.
Duplicating tracks will allow you to also play with the levels of each track through out the entire song and you can accentuate (pan) some parts to create different effects on the final mix.
You can always check the MixPad video tutorials from this link https://www.nch.com.au/mixpad/tutorial.html so you can make the most of the program.