Are you kdding me? You are not alone my friend. This is the qunitessential artist's pet-peeve: trying to prove oneself or validate one's existence through his talents, and the expectations we set on ourselves based on the second conscious. (The voice of other's in our head judging our accomplshments). It's somethig you feel; not hear: the fear of failure.
The trick is to learn to love yourself and your work. And as Nike says, "JUST DO IT". Once you get to the point where you're in it to win it based on how YOU feel about it, you're one step closer. It matters not what other's will say until you yourself are happy with it. And if you like it but they don't, screw 'em. They can't take that away from you.
Again, pointing to the Nike slogan, it's very important to guage progress and achievement for a given project. You can't realistically work on it forver, because you grow as you go; you're very, very likely to lose interest or even touch with the project (Lucas' Star Wars Episode 1 for example). A good idea is to set realistic milestones: little achievement marks or points along the way that you can earn efficiently and in a timely manner. Pat yourself on the back for each one accomplished. It is also imperative that you set some sort of deadline for the finished piece, so that your egging yourself on to finish it.
As my physics instructor used to say, "Don't just sit there -- DO something." Make your move; even if it's the wrong one -- less thought more action... all that good stuff. It's so true. Let me tell you,potential employers want to see conclusion -- they want to see things finished. It doesn't even matter the content, if you can make it clear to them you accomplished SOMETHING, they'll be all the more impressed, because they'll see you as a disciplined and dedicated individual.
You're never gonna do it right until you do it wrong. We learn from our mistakes and build on our experience this way. And you can always, always learn something new.
My advice to you is to just keep up the work on it and guage the milestones you set for it. Note how many milestones you've accomplished after awhile and guage further how realistic it is that some of your ambitions will be met. If not, (and this is the hardest part), you're going to have to settle for stripping it down, or compromising in some way (What Slayer did).
If you feel your in some sort of mental block and just can't make real on any ideas, WALK AWAY from the project for awhile and try to refuel your creativity with games, movies, TV, Books, or even another project (just don't get too carried away with the new one) Maybe set a maximum amount of time alotted to the new one before you go back.
The most important thing to remember: you can always fix it later.
Now if I could just practice what I preach