I dunno man, I'm not really much of a production supremo, I'm sure you know more about it than me, just thought you'd appreciate the feedback and that somebody else may be able to help with the specifics (somebody who is better at this kid of thing than me) - tell you what I'll hook up the link to a mate of mine who knows his way round production kit better than me and I'm sure he'll be able to give some feedback on why it's clipping like that... I dunno maybe it's something simple like rolling back all the levels a bit and fucking with input/putput volumes... Just in case he asks what did you make it on?
With regards to mastering, It's fairly expensive so I'd hold off on that for now as if you get it signed the record label should be able to help out with that...