The way they ended it lets you form the conclusion on your own. It's obvious that "i'm goin back to work" symbolizes that he's goin to make money to get studio time for his demo on his own. I think the movie is solid. Comedy, drama, suspense, etc. all in one.
People are just hatin on it because they wanted to see it end with him recordin his demo, but that's not what the movie is about. It's about him overcoming the fear of being the white rapper that lives in the trailer parks.