I don't think you would be more confident and less shy if you were taller. You'd just shift the perceived problem to another aspect of yourself.
The problem isn't that you're short, but that you lack confidence in the first place which you are trying to blame on the fact you're short... 
Granted, when you perceive something as an error or a flaw, you are more likely to be anxious about it, but it seems most likely that you are anxious and so look for a reason, because you know it's unreasonable...
We all know that SP/SA/Shyness is unreasonable, or rather um.. My mind's gone blank and I can't think of the word lol...  Something... Which is why we try to look for some cause, some reason, something to blame it on... Like you, with relation to your height.
Some people transfer it to the way they look, or their weight, or their voice etc... It's about trying to put our problems onto something defineable, something tangible rather than purely mental...
And I know from my own experience that this is true... I've been over-weight all my life, definitely a flaw, definitely something I can fix and am fixing... I've blamed my weight for the lack of confidence I have, since I was bullied throughout school... However, during the process of fixing it, I was sure my confidence would increase... It's not. Not even the slightest bit... 
That's with a flaw that can be corrected. You can't fix height. But the same still applies. With SA/SP/Shyness, we are that way, not because of physical things, but because of mental things. We just look for reasons which we can see, which are tangible...