I’ll have to agree with InspiringSound here. It’s a wonderful composition and a pleasure to listen to. I think the volume of the piano is fine, and I don’t feel there’s any distracting dissonance (certainly not enough to warrant a hard rejection), but there is one thing that stands out, and it’s the drum kit.
The drums sound quite bright, sharp and mechanic in contrast to the soft, smooth feel of the track. Consider using some softer samples, or even just some light percussion like shakers, etc.
The electric guitar sounds great, as is the fiddle / violin. Is the acoustic guitar live or from a sample library? It sits well in the track, though strums don’t sound entirely realistic to me.
The mix sounds fine to me, though the drums are what mainly let the track down. They sound like strong, high-velocity hits made to sound quiet, which doesn’t sound right. What would be better is to use some low-velocity, softer hits and make them loud enough to fit the volume of the rest of the track.
I would definitely keep working on this track as it has a lot of selling potential; once the drums are in check and everything is balanced out, upload the new version.
Best of luck