The twists should always be tight towards the loops - which is "build in" when doing the loops. The main body of the string should not have any twist in it at this point - but all bundles and strands lying parallel.
Now, by slightly twisting the whole thing in the "tightening" direction given by the twist of the splice - you tighten the main body also - and the splice some more. It should be nice and round all the way - with one complete turn to 1" or 2" is enough and makes for best performance.
I've often used the pic below to explain, because it can be seen quite nicely from the different colors there
Obviously, you seldom get a string which will met this disired stage at propper brace height, so you may twist it tighter to shorten it.
Did you twist it into the opposit direction as with which it was made? The splice will give away then and you are in DANGER! Be carefull not to risk an eye when that thing goes off!
It may be, that the center serving holds some twist back at the lower limbs part of the string if "untwistet below the point" at when it was served on. Is it this what you mean?