UR12 Phones output - Mono or Stereo

I’ve noticed while recording myself playing guitar with a backing track that the levels are really off while monitoring through the phones output on the UR12. The backing track in particular is always really distorted. Today, when I decided to record left and right tracks, I noticed that they were much louder than a centre track. I thought this might mean that the output is mono and that’s what is causing my problem. I’ve been holding off on buying monitor speakers, but maybe it’s turned into a necessity and I can monitor through the left and right outputs on the back of the interface.

Can anyone please provide me with some assistance?