I think a certain amount of stress and fear is an intentional part of the stack exchangeStack Exchange experience. Every time you post, you essentially open yourself up to criticism and comment by the entire userbase. That's a daunting thing, especially if you don't feel like you're an expert yet.
But it's also part of what makes the site work, what causes people to put their best foot forward when answering and asking, and what incentivizes them to come back - that rush of excitement when your answer is well recievedreceived and helps people and you see that with a little bit of rep thrown your way, and that's one of the reasons why people spend their incredibly valueablevaluable free time doing what is essentially professional work for free.
So, relieving the stress won't really work. You have to learn to incorporate it into your process of contributing - make sure your content is up to scratch and take improvement suggestions.