Try this: When you come to a stop, manually use your brake controller to do most of the stopping.
Also, as mentioned earlier, you need to travel at least a couple of trailer lengths to be sure you are straight.
If the brakes aren't adjusted tight enough, it will push off one side or the other every time during a stop. And until you go fast enough to get the trailer to pull back (wind resistance) or you pull a slight hill, it is very possible it will stay off center till then.
If the head pivots freely when you aren't hooked up, and the strut bars are snug when hitched, you should be good to go.
Oh, and don't forget the grease on the strut bar ends. You can't have enough of it. And go ahead and buy some extra of the special zerk fittings. You'll need them. :-)