Playback of MP3 files not balanced
I can't think of anything in EW that would cause that issue, it sounds more like the MP3's themselves or your sound system.
Try them with headphones. If it's balanced right and left fairly evenly, it's quite possible that your sound system is configured as a MONO system instead of a Stereo system (quite common for Churches as they really don't work well as Stereo). You can try to use the PAN control on the mixer to see if you can balance it out, but depending if the system is a MONO system you might not be able to do that. Without knowing EXACTLY what sound equipment you have and how it's all connected it's going to be difficult to diagnose over a forum. Even with that information it would be difficult to do that without being there in person..
Trying to play stereo mp3 sound files in easyworship presentations as background music. They come out but only one sided like singers are lower level than music