I disagree with Urban Dictionary[1] on that definition. An entrepreneur who is trying to succeed, but has not, is just an unsuccessful entrepreneur. The negative context is what embodies the "wannabe" in "wantrepreneur", like "gangsta" and "wanksta". It is an insult. The person using the term thinks you have the desire to be seen as an entrepreneur, but neither the skills, nor the inclination, to actually build anything.

[1] http://www.urbandictionary.com/define.php?term=wantrepreneur