Hmm sounds like you've been holding a very predetermined ideal of your future in your mind. One that appears to have caused you quite a bit of stress and anxiety it would seem.
I wonder why it is you you find the need to hold such an idealized notion of who you are, or rather who you should be? Clinging to such an image makes me think it is forced on you, by you or not, or it arises from a lack of direction from yourself. Your 'identity crisis' might be a result of this image having become to disconnected from who you actually are. Do you feel the need to project an image of yourself to avoid judgement? Do you have a tendency to wear many masks in social situations?
You also appear to be afraid of failure, failing to meet the goals of your idealized image of yourself. Do you feel others hold you to a high standard? Your parents? Do you push yourself to achieve, yourself? Being afraid to fail is normal, but not to the point it cripples you. The best approach imo is simply take things as they come and try to remember to enjoy the ride. Best you can do when you fall is get back up and learn from your mistakes. Things never go perfectly for anyone, and for some things just go horribly badly, but to worry to much about it is a self fullfilling prophecy.
Concluding I'd say the question you must ask yourself is not 'how not to mess up my life' but 'how to worry less about messing up my life'.