Whilst on the right path, perhapse relax isn't quite the right word.
Don't "try". Trying too hard is usually the problem. Try not to do it. Come at the problem from the other side.
There's a logic gene missing from fly fishermen. If you put your hand in a fire and it's hot you pull it out! Logic wins!
But If a cast is going out wrong, it must need a little bit more, it's collapsing. So your average fly fisher adds a bit more power. it doesn't work... so they add a little bit more power and it gets worse, so they add a bit more power (usually till they are purple.) But logic says that at the very first try, they should have done the opposite. adding power didn't work so I must reduce power. But no one *ever* does.
Next time it goes wrong, attack from the rear. Try and make the cast without trying in the slightest. With so little power it couldn't possibly work then add a tiny bit more and a tiny bit more (lets say 10% of what you would usually cast with) and chances are, unless you are making some really fundamental mistakes) the line will go out.
Less is always more in fly casting. if you arewn't using enough power to upset the rod (creating casting problems) then you can't upset the rod.
C