Dan,
It sounds to me like you were trying to recreate the jazz club experience where the acoustic bass player would be standing off center. I think your mix was just a bit too wide for the effect your were after.
I'm still learning myself - it's a never ending process. I'm not as good as I want to be but I'm better than I used to be. And I don't think this sounds as bad as you seem to think.
On eq - drop 400 by 2 or 3 db and it'll brighten things up without having to add higher eq. Remember mixing is a matter of taste. On some things I like a slightly "darker" or "warm" sound. Too much high end can be ear fatiguing.
Did you use the highest bit rate for your mp3? I've never rendered to wma but I've heard some great mixes on here done that way.
Hang in there. You can learn. You're not off to that bad of a start.

Editted to add: looks like you got some great advice while I was typing this. LOL!
Josie