You're going to have a bit of doubt when getting married, most people (most, not all) generally do when they're afraid/not sure of what's going to happen. It's only really natural, in all honesty. There are so many things happening with you and your fiance that you probably would benefit greatly from stepping back and looking at the situation as an outsider. Just try not to rush things, and look at all the possible questions that might come up in the near future. For instance:

• Can we financially make ourselves stable?
  
• Will he eventually find a job that he holds?
  
• If we run into trouble (debt, etc.) do we have options to help us?
  
• Will these problems tear us apart down the road?
  
• Will he eventually be willing to do things without you asking?

As for getting him more mature, these things aren't really a learned concept especially as we grow older. It will take him and perhaps you calling him on some things for him to realize that there is actually something going wrong. He will eventually come around, but as long as you don't show him that he needs more responsibility and commitment, he most likely will continue acting in this manner. Just a suggestion, but: If you say you want to postpone the wedding, maybe this will get him to realize there is something wrong. It will easily open up some dialogue between the two of you. This may also just show him/shove him down the path that he needs to be looking towards. :)

Good luck, and I hope everything turns out great for the both of you.
~Wayne

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