Loosen the two screws where the highback connects to the base. Hold the highback in the position where you want it. Tighten the two screws while holding the highback in place.
In the future if you're having trouble fitting the board into a bag just unmount the bindings, you can either pack them separately or mount them on the board at an angle that won't let the highback overhang the edge. Just remember to take a screwdriver with you so you can remount them at your regular angles when you get to your destination.
Depending on how big that gap is, you should be fine. I've got the same thing on my P1.1s but it's only a 1/16th of an inch or so on the one side, and the gap closes when pressure is applied back on the highback.
No, it should move back and forth freely. You have one side pushed too far back. Loosen one screw, and move it slightly forward until it moves freely.
As suggested, next time you take your board somewhere, remove the bindings completely. It's much easier to reinstall them that way and get them perfectly where you want them than it has been for you to reinstall the highbacks.
Originally Posted by Stephen Hawking on Pink Floyd's "Keep Talking"
For millions of years, man lived just like the animals. Then something happened which released the power of our imaginations. We learned to talk."